Central heating questions

edited 30 November -1 at 1:00AM in Energy
24 replies 7K views
Phil3822Phil3822 Forumite
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edited 30 November -1 at 1:00AM in Energy
Hello all, I have recently had central heating installed having removed storage heaters. This is the first time we have had gas central heating in a home and want some guidance on thermostat usage.

The thermostat is in the hallway, currently it is set to 16c, the living room temperature currently is around 21.5c which is perfect. The bedrooms however are a little cool. As we have a teenager there is one bedroom in use rather often.

I assume I should turn the thermostat up in the hall and then turn the radiator thermostats down on the living room radiators. I expect this would be less efficient though.

I should note the thermostat is a hive one and although attached to the wall can be moved about.

I think I need to learn a bit more about typical usage and setups. Any thoughts would be great.
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  • FarwayFarway Forumite
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    First off, has your new system been "balanced"?

    If not do that. It can be a bit of PIA

    https://www.homebuilding.co.uk/how-to-balance-radiators/

    other guides are available via Google
  • My thermostat is a normal fixed on & sits at the bottom of the stairs (Victorian two up/two down type house) on the party wall. I have to set it at 18 degrees for the rooms to be comfortable at 21 degrees cos the wall it's attached to is colder than air temp & heat has to pass through the hallway. TRV's control the temps in the big & small bedrooms.
    Took a fair bit of guess work to get it right for the whole house...
  • Phil3822Phil3822 Forumite
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    Thanks for responding. It is all balanced.

    The thermostat is in my hall on the outside wall. The hall is colder and less well insulated the living room so I not surprised at needing it to be a lower temperature. To get the room upstairs warmer I guess I will have to turn the main thermostat up and then turn the living room ones down to keep it at 21c.

    Only been installed a week so getting used to things, want it efficient but effective. Thanks again.

    Ps, as the hall looses heat much more easily than the living room I note I have to adjust it daily. Multiple windows and doors in hall. Thanks.
  • SystemSystem Forumite
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    Phil3822 wrote: »
    Hello all, I have recently had central heating installed having removed storage heaters. This is the first time we have had gas central heating in a home and want some guidance on thermostat usage.

    The thermostat is in the hallway, currently it is set to 16c, the living room temperature currently is around 21.5c which is perfect. The bedrooms however are a little cool. As we have a teenager there is one bedroom in use rather often.

    I assume I should turn the thermostat up in the hall and then turn the radiator thermostats down on the living room radiators. I expect this would be less efficient though.

    I should note the thermostat is a hive one and although attached to the wall can be moved about.

    I think I need to learn a bit more about typical usage and setups. Any thoughts would be great.

    If you have TRVs in all your rooms and a thermostat in the hall then effectively your thermostat is nothing more than an ON/OFF switch for the boiler. If you have it set at 16C, and this temperature is reached, then your boiler will shut down. I have 19 radiators - all with TRVs - plus a pump automatic bypass. All room temperatures are set as required on the TRVs. The hall stat is set at a temperature which will not result in the heating switching On and Off. Leaving the heating on is the most efficient way of running a modern condensing boiler. The boiler will stay in a condensing temperature range and modulate down to cater for the Hive calculated TPI demand. As I post, my 5 bed home is on temperature and my gas usage is 0.1CM3s every 15 minutes (about 12p/hr). My boiler currently has a demand flow temperature of 55C and a return temperature of 40C. With a new CH system - and properly sized radiators - you should be getting a flow/return differential of c.20C. The radiators should be warm rather than hot.
  • nxdmsandkaskdjaqdnxdmsandkaskdjaqd Forumite
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    Hengus wrote: »
    With a new CH system - and properly sized radiators - you should be getting a flow/return differential of c.20C. The radiators should be warm rather than hot.

    I balanced my system a few years ago when I changed to a condensating boiler. I found that when the boiler was starting up from cold and on full power (not modulating) I would obtain a 20 C differential across all the radiators. However, when the boiler has gone in to modulatation mode I would obtain a 12C differential.

    The boiler has 55c flow and 43c return.

    Do you not have to be mindfull of the boiler status when performing these balancing tests?
  • edited 29 December 2017 at 6:00PM
    SystemSystem Forumite
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    edited 29 December 2017 at 6:00PM
    I balanced my system a few years ago when I changed to a condensating boiler. I found that when the boiler was starting up from cold and on full power (not modulating) I would obtain a 20 C differential across all the radiators. However, when the boiler has gone in to modulatation mode I would obtain a 12C differential.

    The boiler has 55c flow and 43c return.

    Do you not have to be mindfull of the boiler status when performing these balancing tests?

    It sounds like you have added a condensating boiler to an existing heating system. (As indeed, have I). The ‘problem’ is that your radiators are most likely now undersized. Non condensing boiler/heating systems are normally balanced to a differential temperature of 12C. Condensing boiler/heating systems should be balanced to a 20C differential. I decided that the cost of replacing some of my radiators was not justified when future savings were taken into account.

    As explained to me by a very knowledgable installer, the reason you are getting 20C differential on start up is because there is a lot of water to heat up. As the radiator temperature rises, and rooms reach temperature, the boiler modulates down to its lowest level. My boiler modulates from 24 down to 5 Kw but even this is too much for my system with TRVs closed. In other words, the effective heating area is too small for a 5Kw flow and the return temperature comes back at less than a 20C differential. This is why some installers are not persuaded that there is any need to fit TRVs ( and if fitted, they should be left fully open).
  • nxdmsandkaskdjaqdnxdmsandkaskdjaqd Forumite
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    Hengus wrote: »
    It sounds like you have added a condensating boiler to an existing heating system.

    My boiler modulates from 24 down to 5 Kw but even this is too much for my system with TRVs closed. In other words, the effective heating area is too small for a 5Kw flow and the return temperature comes back at less than a 20C differential. This is why some installers are not persuaded that there is any need to fit TRVs ( and if fitted, they should be left fully open).

    Yes you are correct, an old system with a new 30kw condensating boiler.

    I have the same problem with the TRVs set in that the 5KW in modulation is too much for the system, so the boiler shuts down. I now leave most of the TRVs fully open and have a room stat in the hall.

    Knowing what I know now I should have not gone with a 30kw boiler, something like 20kw would have kept the system in modulated mode all the time.
  • Phil3822Phil3822 Forumite
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    Hengus wrote: »
    If you have TRVs in all your rooms and a thermostat in the hall then effectively your thermostat is nothing more than an ON/OFF switch for the boiler. If you have it set at 16C, and this temperature is reached, then your boiler will shut down. I have 19 radiators - all with TRVs - plus a pump automatic bypass. All room temperatures are set as required on the TRVs. The hall stat is set at a temperature which will not result in the heating switching On and Off. Leaving the heating on is the most efficient way of running a modern condensing boiler. The boiler will stay in a condensing temperature range and modulate down to cater for the Hive calculated TPI demand. As I post, my 5 bed home is on temperature and my gas usage is 0.1CM3s every 15 minutes (about 12p/hr). My boiler currently has a demand flow temperature of 55C and a return temperature of 40C. With a new CH system - and properly sized radiators - you should be getting a flow/return differential of c.20C. The radiators should be warm rather than hot.

    Thanks for this info. I had an atag 35i economiser with 8 radiators in a 3 bed semi. Water temp set to 65c but no idea how to test return temp.

    I assume you set your hall thermostat high to keep the boiler working all the time, then have your water temp lower and use the TVR's. Me paraphrasing to make sense as I am unsure.

    My hall radiator has no TVR. I really could do with learning more from you, I want an efficient system and warm home but am very new to this all.
  • SystemSystem Forumite
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    Phil3822 wrote: »
    Thanks for this info. I had an atag 35i economiser with 8 radiators in a 3 bed semi. Water temp set to 65c but no idea how to test return temp.

    I assume you set your hall thermostat high to keep the boiler working all the time, then have your water temp lower and use the TVR's. Me paraphrasing to make sense as I am unsure.

    My hall radiator has no TVR. I really could do with learning more from you, I want an efficient system and warm home but am very new to this all.

    I have an Atag is24 system boiler which is controlled by an Opentherm bridge. The boiler profile is set to a TMaxSet temperature of 70C. The boiler display can be cycled through a variety of settings: A0 is TSet Max flow temperature ; A1 is the the return flow temperature and, perhaps the most important one is A3. A3 is what is known as TSet (Calculated). With my controls, the TSet Calculated temperature is determined by the Opentherm Bridge based on the total heat requirement for the system. Whenever there is a hot water heating demand, the TSet Calculated temperature will rise to 70C. With just heating, the boiler will modulate and the TSet Calculated will fall automatically with the boiler attempting to achieve a 20C differential.

    Your boiler guide is here. Have a look at Page 9 for boiler information temperature information. You just cycle through the menu.


    http://atagheating.co.uk/wp-content/uploads/2017/10/ATAG-USER-INSTRUCTIONS-i-Range-0117.pdf

    I monitor my gas usage in 15 minute segments with a silver dot optical reader. This has shown that with my boiler and controls there is no advantage in turning down the heating if I am out for less than 3 hours: the gas usage getting the system back up to temperature exceeds the saving if I turn the thermostat down by 3 degrees. I suspect that this is down to Honeywell’s controller fuzzy logic and Opentherm. With a 2 degree difference between the target and actual temperatures, the thermostat will demand a flow temperature of 70c which takes the boiler out of the condensing mode. This is not as daft as it sounds as most people want their property to heat up quickly rather than efficiently.

    I suspect that your hall radiator has no TRV as the installer has not fitted an automatic bypass valve (ABV). An ABV or open radiator is needed as most boilers have an over-run when heat demand ceases. This is to avoid damage to the boiler. It is somewhat unusual to choose the hall radiator: most installers will either fit an ABV or leave the radiator in a bathroom on open flow to dry towels etc.
  • Phil3822Phil3822 Forumite
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    Thanks again, is there anything to say when the boiler is in condensing mode? I take it my hive set up is a simple on and off type. I was tempted by the atag one. I will play about with the boiler buttons to view readings. When am I best to do this? I don't really understand what the A3 is, is it the current water temperature rather than max which A0 shows. Nice to see a fellow atag user. I like to understand all the things in my home where possible.
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