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    • marks87
    • By marks87 6th Oct 16, 12:06 PM
    • 146Posts
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    marks87
    Help me understand our central heating!
    • #1
    • 6th Oct 16, 12:06 PM
    Help me understand our central heating! 6th Oct 16 at 12:06 PM
    We had a brand new central heating system installed at the start of the week, and it's the first time we've had CH (old house + lack of funds =ed costly electric ).

    Anyway, the plumber explained the basics of how the system works and how you control the temperature. But we're still not entirely sure how to get the optimal settings for the whole house, so I was hoping someone on here could explain in reasonably simple terms!

    We have radiators throughout the house with TRVs, except in the living room where the thermostat is - I believe this is normal, yes? We can then set or programme a temperature for the boiler to then kick in and start heating the house. The TRVs can then be used to control the temperature in the other rooms. That's straightforward enough.

    What's confusing is is what happens if, say, we have visitors and the living room gets warm enough to cut the boiler based on the temperature detected by the thermostat? Does that mean the rest of the house will be cold because the living room is too hot? If so, what's the solution? Or have I completely misunderstood.

    My gut feeling is that the system must work to heat the whole house somehow, including hotter and colder rooms - otherwise, nobody would ever want it. But being CH n00bs, we don't quite yet understand it!

    The thermostat we have is a Worcester Wave, if that makes a difference to how things work.
Page 1
    • CashStrapped
    • By CashStrapped 6th Oct 16, 12:57 PM
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    CashStrapped
    • #2
    • 6th Oct 16, 12:57 PM
    • #2
    • 6th Oct 16, 12:57 PM
    You are nearly there....but not quite.

    Welcome to the world of on demand heating!

    These are the controls you are most likely to find on your system and how they work.

    1) Controls on the Boiler itself. These controls will determine the temperature the water is heated to. On a combi, usually one for heating, the other for hot water to taps. In terms of Central Heating, the temperature of the hot water running through the radiators affects how quickly a room or rooms will heat up. (see combi boilers/condensing boilers side note below)

    2) Whole house thermostat. This does not control the water temperature or anything like that. It simply tells the boiler to turn off once the room temperature (wherever it is situated) has been reached.

    So to give an example of those two working together. If you have the boiler water temp on very high. The radiators may get red hot and warm the room up very quickly. At which point the thermostat will cut of the boiler when the room reaches the required temperature.

    3) TRV valves. These again monitor the temperature of the room. Depending on the setting on the TRV, these will cut off the supply to the radiator while the room is at the desired temperature. It does not stop the boiler from running, but allows a room to be bypassed to give the boiler an easier time heating other areas. If the room cools too much (depending on the setting) the supply to the radiator will be restored.

    Thermostat side note: You are correct in that if the whole house thermostat is put in a warm room then the heating to the rest of the house may be shut off. This is because the boiler thinks the whole house is at that temperature. A thermostat should ideally be placed in an area in the house which gives a decent average temperature (this is why they were usually placed in hallways, but away from the front door). Another solution to this is to get a decent wireless thermostat (honeywell are a good brand). This will allow you to place the thermostat anywhere in the house. You can then find a good place for it.

    Combi boilers side note: Modern combi (or any modern condensing boiler) boilers work more efficiently when the system is used at the lowest temperature (controls on the boiler) possible to keep the house warm. Therefore there is an incentive to run the central heating system at a warm temperature for longer rather than very hot for a short period(s). This is because it allows the condensing part of the boiler to recover more waste heat. This will improve boiler efficiency. This only happens at a lower temperature.

    I hope that helps!
    Last edited by CashStrapped; 06-10-2016 at 2:49 PM.
    • marks87
    • By marks87 6th Oct 16, 1:27 PM
    • 146 Posts
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    marks87
    • #3
    • 6th Oct 16, 1:27 PM
    • #3
    • 6th Oct 16, 1:27 PM
    OK, I think I've got that. Thanks.

    The plumber fitted the thermostat to the living room wall. The living room is usually average, but can get warm if we have visitors.

    Would I be right in thinking that it's best to leave the living room door open as much as possible? Obviously we've been in the habit of having it tight shut to keep the heat in, but with central heating I guess the aim is to let the heat spread as much as possible to heat the house as opposed to individual rooms.

    Is it also the case that we need to give the system time to "bed in", maybe once the (really) cold weather starts? We also have triple glazing and insulation so I'm thinking that once the system properly house once, the radiators will then just simmer along nicely to maintain the heat.
    • CashStrapped
    • By CashStrapped 6th Oct 16, 1:43 PM
    • 857 Posts
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    CashStrapped
    • #4
    • 6th Oct 16, 1:43 PM
    • #4
    • 6th Oct 16, 1:43 PM
    I do not see why a system would have to "bed in" in any way.

    In a modern property a wireless thermostat would be the best solution if you are having issues with maintaining a consistent temperature for the thermostat.

    If leaving the door open gives a more consistent temperature then that is fine but I can imagine it getting a bit annoying.

    It is all about temperature consistency for a thermostat to work best.

    There is no method behind heating the house well to get it warm once, then letting the radiators simmer.

    All houses will lose heat in relation to their individual insulation specification. This will be at a specifics rate of heat loss. So, you will in time get used to how quickly your house loses heat, what is comfortable for you and so on. You can then set the boiler controls and timers accordingly. As per above, the lower the radiator temperature that you can achieve this with, the more efficient your boiler may run.

    Basically, all heating is, is replacing warm air faster then your property loses it.


    In addition, now you have central heating and a nice insulated house. Never dry clothes on your radiators. If you have a tumble dryer, use that or a line. Otherwise you may get massive damp problems. This would be more apparent in a well insulated house as all the evaporated water from your clothes is trapped inside the house. It will eventually condensate on cold spots on walls and eventually cause damp and mould. Ensure you have good ventilation in the kitchen and bathrooms. People do not realise, the more you insulate the more you need good, controlled, ventilation.
    Last edited by CashStrapped; 06-10-2016 at 2:34 PM.
    • Cardew
    • By Cardew 6th Oct 16, 2:59 PM
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    Cardew
    • #5
    • 6th Oct 16, 2:59 PM
    • #5
    • 6th Oct 16, 2:59 PM
    What's confusing is is what happens if, say, we have visitors and the living room gets warm enough to cut the boiler based on the temperature detected by the thermostat? Does that mean the rest of the house will be cold because the living room is too hot? If so, what's the solution? Or have I completely misunderstood.

    My gut feeling is that the system must work to heat the whole house somehow, including hotter and colder rooms - otherwise, nobody would ever want it. But being CH n00bs, we don't quite yet understand it!
    Originally posted by marks87
    You haven't misunderstood. With a fixed room thermostat it is often impossible to heat up other rooms because that room(the living room in your case) is too hot.

    A partial solution is to buy a wireless thermostat that you can move from room to room, but if you move it to, say, the hallway other rooms will heat up, but in your case the living room will continue to heat up even more as you don't have a TRV on the radiator in the living room.

    There is no ideal situation, it is all a compromise.
    • reeac
    • By reeac 6th Oct 16, 5:07 PM
    • 953 Posts
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    reeac
    • #6
    • 6th Oct 16, 5:07 PM
    • #6
    • 6th Oct 16, 5:07 PM
    My experience is that there is a fair amount of diffusion of heat throughout a building thus spreading the heat around even if a radiator is off. We live in a bungalow and so have no convection from downstairs to upstairs but our bedroom which we practically never heat (through preference not for economy) never gets really cold ....maybe 12-14 C when the hall thermostat is at 20C. Have you actually found from experience that you get this "visitor effect" in just a few hours?
    • teddysmum
    • By teddysmum 6th Oct 16, 5:21 PM
    • 5,819 Posts
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    teddysmum
    • #7
    • 6th Oct 16, 5:21 PM
    • #7
    • 6th Oct 16, 5:21 PM
    We have a wireless thermostat that I specifically asked to be left portable and we choose to keep it in the living room as that is the room most used. The radiator valves in other rooms are appropriately turned down, with the bathroom one being turned up when anyone intends to have a bath.


    You will know that the thermostat is set with a choice of temperatures over a number of time periods (setting overnight much lower), but it is possible to override a set temperature just for the duration of the current period. (eg for a 9am to noon setting, you could drop the temperature by 2 degrees , but it will revert to the permanent setting after noon, when you can again alter the setting, if you wish.)
    • bsod
    • By bsod 6th Oct 16, 5:29 PM
    • 1,065 Posts
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    bsod
    • #8
    • 6th Oct 16, 5:29 PM
    • #8
    • 6th Oct 16, 5:29 PM
    Your thermostat is in the wrong place.

    cheapest solution is to up the temp of the thermostat, and move a trv from a cold room (eg hall, bathroom) to the living room, or adjust the valve yourself if too hot.

    Also, all rooms don't need to be the same temperature, so you may want your living room at a higher temperature than the bedrooms anyway.
    Last edited by bsod; 06-10-2016 at 5:43 PM.
    • Cardew
    • By Cardew 6th Oct 16, 5:36 PM
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    Cardew
    • #9
    • 6th Oct 16, 5:36 PM
    • #9
    • 6th Oct 16, 5:36 PM
    We have a wireless thermostat that I specifically asked to be left portable and we choose to keep it in the living room as that is the room most used. The radiator valves in other rooms are appropriately turned down, with the bathroom one being turned up when anyone intends to have a bath.


    You will know that the thermostat is set with a choice of temperatures over a number of time periods (setting overnight much lower), but it is possible to override a set temperature just for the duration of the current period. (eg for a 9am to noon setting, you could drop the temperature by 2 degrees , but it will revert to the permanent setting after noon, when you can again alter the setting, if you wish.)
    Originally posted by teddysmum
    But the dilemma facing the OP(and others) is that when his living room is up the temperature he requires, there is no heating to the rest of the house because the heating is switched off by the room thermostat..

    Getting a wireless thermostat and moving it to a cooler part of the house will start up the heating, but his living room will then get even hotter because he can't turn off the radiator.

    In your case where you 'chose to leave the wireless stat in the living room'
    you will face exactly the same dilemma in heating your bathroom when the living room is at the required temperature.
    • Cardew
    • By Cardew 6th Oct 16, 5:39 PM
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    Cardew
    Your thermostat is in the wrong place.

    cheapest solution is to up the temp of the thermostat, and move a trv from a cold room (eg hall, bathroom) to the living room, or adjust the valve yourself if too hot.
    Originally posted by bsod
    I tend to agree, but it is now mandatory in new systems for the radiator in the room with the thermostat to have no TRV.
    • lstar337
    • By lstar337 7th Oct 16, 11:50 AM
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    lstar337
    I tend to agree, but it is now mandatory in new systems for the radiator in the room with the thermostat to have no TRV.
    Originally posted by Cardew
    When did this come in Cardew?

    I only ask because our house (built 2014) has a TRV on the rad in the hall, the same room as the thermostat. I always thought it was odd, but it doesn't bother me because I leave it on full anyway.

    My only thought was that maybe our boiler doesn't require at least one rad to be always open, maybe it has the ability to divert through an internal loop or something.
    Last edited by lstar337; 07-10-2016 at 4:57 PM.
    • CashStrapped
    • By CashStrapped 7th Oct 16, 2:02 PM
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    CashStrapped
    I think that is the main technical reason (what you suggested) Istarr337. That one rad should not have a TRV so there is always some guaranteed flow.

    But I also think that is considered inadvisable (maybe just guidance) to put a TRV in the same room as the stat because, in an enclosed space, they may interfere with each others operation.

    The TRV may cut off the radiator (if set at a different temp), so the room stat may think that the room is not up to temp and keep the heating on. The rest of the house would then get very hot. Obviously that is just one permutation of what could happen.

    Your hallway may be open enough and have enough air movement to avoid this happening.
    Last edited by CashStrapped; 07-10-2016 at 3:02 PM.
    • Cardew
    • By Cardew 7th Oct 16, 4:17 PM
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    Cardew
    When did this come in Cardew?

    I only ask because our house (built 2014) has a TRV on the rad in the hall, the same room as the TRV. I always thought it was odd, but it doesn't bother me because I leave it on full anyway.

    My only thought was that maybe our boiler doesn't require at least one rad to be always open, maybe it has the ability to divert through an internal loop or something.
    Originally posted by lstar337
    I assume you mean 'same room as the thermostat??

    I have seen the regulation about TRVs on loads of websites e.g.

    http://www.ukplumbersforums.co.uk/central-heating-forum/46092-trv-valves-room-thermostat-compulsory-new.html

    I have TRVs on every radiator. This enables me to control the temperature in every room in the house with a TRV. However if 2 or 3 rooms are in use, it means moving the wireless thermostat from room to room if one room is up to the required temperature.
    • lstar337
    • By lstar337 7th Oct 16, 4:58 PM
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    lstar337
    I assume you mean 'same room as the thermostat??
    Originally posted by Cardew
    Yeah, sorry.

    I have TRVs on every radiator.
    Originally posted by Cardew
    Same here. I just wondered if there was something non-standard about my installation.
    • Cardew
    • By Cardew 7th Oct 16, 5:15 PM
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    Cardew
    Yeah, sorry.

    Same here. I just wondered if there was something non-standard about my installation.
    Originally posted by lstar337
    The reason for having one radiator without a TRV is to still have a flow when all radiators are off(TRVs up to temp)

    You, like myself, will have an automatic bypass valve.

    http://www.honeywelluk.com/products/Valves/Bypass-Valves/DU146-Automatic-Bypass-Valve/

    The DU146 saves energy by only allowing flow through the bypass when needed i.e. when flow through the system is reduced when zone valves or radiator thermostats are closing. The use of an ABV is recommended by the UK government as Best Practice in the CHeSS (Central Heating System Specifications) guide to central heating systems.
    Last edited by Cardew; 07-10-2016 at 5:18 PM.
    • matelodave
    • By matelodave 7th Oct 16, 5:20 PM
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    matelodave
    Generally if you've got a TRV in every room the system should have a bypass valve which maintains flow through the boiler until it shuts down.

    Ideally you should leave the TRV fully open when there's one in the same room as the main system thermostat as you'll get the situation as outlined by Cashstrapped above.
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    • ASavvyBuyer
    • By ASavvyBuyer 7th Oct 16, 5:49 PM
    • 184 Posts
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    ASavvyBuyer
    We have trv's on all our radiators and use a portable wireless thermostat to control the temperature of the room/s we are using. In the room that has the thermostat the trv is turned up to max and in other rooms the trv is either off or set at the required temperature. This works for us and saves us a fortune by not heating the rooms we are not in!
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    • Pincher
    • By Pincher 8th Oct 16, 3:21 PM
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    Pincher
    The art of radiator central heating is a delicate balancing act.

    With "property developers" slicing up houses willy nilly, it takes even more judgement than when you had a simple four bed semi to configure.

    The TRV is not telepathic, all it does is detect the room temperature and shuts off the flow. What you can do is to adjust the other valve on the radiator, called the lock shield valve.

    You can tighten the lock shield valve in the living room, so that the flow is low, i.e. less heat gets to the living room relative to the other rooms. In extremis, you simply close the radiator in the living room, so it is always the coldest room in the house.

    You should always leave a radiator freely flowing, so the circulation pump won't overheat, and eventually die. People say there is auto-shutdown, but it's just good practice not to block the flow totally.
    What happens if you push this button?
    • marks87
    • By marks87 9th Oct 16, 10:01 PM
    • 146 Posts
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    marks87
    Thanks for all the replies and insights.

    It's been slightly colder the past couple of days and we have noticed that when the boiler program kicks in for "high" temperatures (7am in the morning and 5pm in the evening), the heat generated is well retained by the rooms. So even if the radiators aren't "on" because the living room is hot enough, the rooms are still plenty warm.

    I've been looking at the different bits of the Wave app and I was wondering what weather compensation does? The installer mentioned it briefly but didn't go into real detail. Only that this system doesn't have its own external sensor but instead uses several online weather sources to determine the temperature.

    When I look at the settings, there's various things - End and Start point curves, max and min flow temperature and, the one I'm intrigued by, "room influence" - which I can set from "None" through "Low...", "Medium..." and "High temperature system". I'm assuming this is something to do with how much the reading from the thermostat is considered when determining whether to heat? And it's therefore possible to heat the house without over-reliance on the living room thermostat?

    Is using weather compensation recommended? And if so, can anyone shed any light on how it works? I switched it on to see what happened and I noticed the boiler fired up and the radiators all heated up (it's 6C out there just now). It now keeps coming on and off more frequently than before.
    • Cardew
    • By Cardew 9th Oct 16, 10:31 PM
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    Cardew
    All boilers these days are condensing boilers. It is important to understand that they operate most efficiently when they are in condensing mode. There are thousands of websites that explain the principle of a condensing boiler but this is sufficient:

    One of the hot gases produced in the combustion process is water vapour (steam), which arises from burning the hydrogen content of the fuel. A condensing boiler extracts additional heat from the waste gases by condensing this water vapour to liquid water, thus recovering its latent heat.
    !
    An increase of efficiency can be as much as 10-12%.The effectiveness of this condensing process varies, it depends upon the temperature of the water returning to the boiler, but for the same conditions, it is always at least as efficient as a non-condensing boiler.
    To get the water temperature returning to the boiler as low as possible, the output temperature should be as low as possible; and that essentially is the purpose of weather compensation. It senses the outside ambient temperature and adjusts the boiler water temperature.

    Boilers can only condense when the flue gases within the boiler are at their ‘dew point’ of 57°C. So to ensure continuous condensing operation the heat exchange surfaces and therefore the return water must be at this temperature.
    There are two ways to achieve this. Design the heating system so that its return temperature is low (underfloor systems for example). Alternatively control the boiler flow temperature so that it runs as low as possible for the longest time. Letting the boiler automatically ‘ float’ in line with weather demand is the proven approach. Does it matter if you run the boiler at low temperatures? Not for most of the winter. In an average British winter only perhaps 30 days out of 200 are anywhere near the temperature (0°C) that the system was designed to provide for.
    An average winter temperature is around 10°C, so it pays to keep the boiler running at a low figure as long as possible.
    Weather compensation can do this automatically.
    Weather Compensation Explained!
    Weather compensation controls enable a condensing boiler to work at its optimum efficiency. The controls allow the boiler to vary its operating flow temperature automatically, day by day to suit the weather outside and the temperatures inside the house.
    Weather compensation works with a sensor outside and another in the boiler communicating with each other, all the time and varying the boiler's water flow temperature accordingly, rather than the boiler turning on and off which wastes energy.
    The aim is to keep the temperature as low as possible and so the boiler condenses for virtually all of its operating period.
    Fitting weather compensation can increase the efficiency gain of your boiler by 10% and this can all be achieved from as little as £100 extra.!
    Viessmann boilers come with the connections and control on the boiler to make weather compensation a "plug and play" option.
    Click to view the Vitotronic 200 control with weather compensation
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