Confused by how central heating works....

devon_guy

So the title says it all really. What does the thermostat on the boiler do? What about the one that's in the hall and the ones on radiators?

I have a friend that has central heating and she says she leaves it on permanently and just turns the dial up and down in the hall as necessary which turns the heat on and off. Is this right? Is it efficient to do this?

mech_2

devon_guy wrote: »

So the title says it all really. What does the thermostat on the boiler do?

The thermostat on the boiler sets the operating temperature of the radiators when the boiler is on.

What about the one that's in the hall

That one sets the temperature of the hallway. When the hallway is up to the set temperature it turns off the boiler completely even if the other rooms are not warm enough. This is why it's usually put in a room that's difficult to heat as then the other rooms will probably be warm enough by the time the boiler cuts out. Hallways are quite a common choice because they often have a stairwell which carries all the heat onto a landing, and a front door which is probably draughty.

and the ones on radiators?

They set the temperature of each individual room by turning the water off to each radiator. This allows you to keep the bedrooms cooler than the living room, for example. They do not turn off the boiler - that's what the wall thermostat is for (see above).

I have a friend that has central heating and she says she leaves it on permanently and just turns the dial up and down in the hall as necessary which turns the heat on and off. Is this right? Is it efficient to do this?

I do it.

As long as you remember to do it every day it's probably not less efficient than switching it off on a timer. Most houses cool down fairly slowly anyway, so as long as you turn it down far enough the boiler won't come on significantly before you next turn the thermostat up again. It's really just a case of trial and error, because some houses lose heat faster than others.

If you have a heating programmer and a predictable daily routine there's really little point in not using a timer though. I don't have a predictable routine, and I have tested my house to find that it doesn't cost me a lot more even if I leave the heating on fully for 24 hours a day, but most people aren't me (and don't live in my house).

devon_guy

mech wrote: »

The thermostat on the boiler sets the operating temperature of the radiators when the boiler is on.


They set the temperature of each individual room by turning the water off to each radiator.

Isn't that a contradiction? You say the thermostat on the boiler contraols the temp of the rads then you say the rad thermostats control the temps. Sorry for being thick!

so if I left my boiler on constant but turned the hall thermostat down in the hall to its lowest setting in the summer, in theory the boiler would never come on?

Cardew

devon_guy wrote: »

mech wrote: »

The thermostat on the boiler sets the operating temperature of the radiators when the boiler is on.


They set the temperature of each individual room by turning the water off to each radiator.

Isn't that a contradiction? You say the thermostat on the boiler contraols the temp of the rads then you say the rad thermostats control the temps. Sorry for being thick!

so if I left my boiler on constant but turned the hall thermostat down in the hall to its lowest setting in the summer, in theory the boiler would never come on?

No it is not a contradiction.

The thermostat on the boiler sets the temperature of the water that is circulating in the CH system(60C to 82C on my boiler). So the higher that setting, the hotter the radiators get; and thus the room will heat up quicker.

The thermostat on the radiator(a Thermostatic Radiator Valve -TRV) senses the air temperature in the room and when that air temperature reches the set level it shuts off the water supply to the radiator.

If your wall thermostat is set to below the temperature of the room in which it is situated, then the boiler is effectively off. This is Mech's preferred method of control - in effect he uses the wall(room) thermostat as an on/off switch.

Many of us simply put the wall thermostat up to maximum and control the temperature of each room with the TRV. In fact some older CH systems did not have a wall thermostat.

devon_guy

Thank you. I appreciate your help. I think things are becoming a bit clearer now!

thor

Cardew wrote: »

devon_guy wrote: »

Many of us simply put the wall thermostat up to maximum and control the temperature of each room with the TRV. In fact some older CH systems did not have a wall thermostat.

What would happen if you did this but turned off all the radiators via the TRV? Won't all the hot water generated by the boiler have nowhere to go? Maybe this could cause damage?

Cardew

thor wrote: »

Cardew wrote: »

What would happen if you did this but turned off all the radiators via the TRV? Won't all the hot water generated by the boiler have nowhere to go? Maybe this could cause damage?

it wouldn't matter for the majority of systems installed in the last 25 years as they have an Automatic Bypass Valve(ABV). Without an ABV you must have one radiator without a TRV

Automatic Bypass Valve
What is an automatic by-pass valve?
An automatic by-pass valve is designed for use in domestic central heating systems. Its purpose is to maintain constant pump pressure within the system.
Back to top
What are the advantages of an automatic by-pass valve?
An automatic by-pass valve ensures minimum water flow rates through the boiler. It reduces system noise associated with high pressure pumps. It eliminates the need to fit an uncontrolled radiator to act as a system by-pass and it also increases system efficiency. The automatic by-pass valve also aids the operation of thermostatic radiator valves.

thor

where would this abv be? I have a vaillant eco max boiler and was told by the servicing engineer that you needed to leave at least one radiator on to act as a release for the hot water buildng up in the boiler. It is 8 years old so it would have an abv somewhere wouldn't it. Could the engineer have made a mistake in his advice?

david29dpo

The ABV could be in the boiler (check the manual if you have it) of somewhere in the pipework. If you are not sure in any way, as said above, one rad MUST be left open. This could be the one without a TRV if all the others have them.

Debtoxing

Please could I ask for some information too? I am horribly ignorant about plumbing, so please forgive this horribly ignorant question. Our gas and electricity bills are really high, but I can't figure out what to do about them without some help!

I have a hot water tank with an immersion heater, which I understand can be very expensive and could be contributing to our problems. But we also have a gas boiler for the central heating. Would the gas boiler be heating the water in the hot water tank as well as the immersion heater? Why would we need both?

It looks to me as though switching off the immersion heater would also involve switching off the timer (which I've just reprogrammed so that the heating and hot water only come on for a couple of hours a day). Is that probable?

I'd really appreciate any advice - I have a nagging feeling that there's money being wasted here, but I'm too scared to do anything about it in case I blow the house up or something! :eek:

Thank you!

L.
xxx

saintlee

Ok, a few misconceptions here.

Conventional boilers (even modern ones) do not have an automatic bypass, as the central heating pump is not located within the boiler

Most Combi and system boilers do. A by pass is required so when the pump is running, it can always circulate and is not trying to push against a dead end, which will burn it out very quickly.

All modern systems should have aroom stat fitted so as the boiler knows when the house is at the desired temperature.

If there is no room stat, the boiler will only shut off when the water temperate reaches the boiler stat temperature. The problem with this, is that all of the thermostatic rad valves could be satisfied, yet the boiler will keep heating the water that is circulating within the pipework even though none of the radiators are calling.

One common installation fault is that people put thermostatic valves on all radiators. The radiator closest to the room stat should not have a thermostatic valve on, and it's temperature should be governed by the room stat. Otherwise what happens is that the radiator stat can be satisfied and shut itself off, but the room stat is still calling the boiler on.

One common mistake that home owners make is to turn the roon stat up high if they are cold, or down low if they are hot.

This isn't how they work. The room stat will call the boiler on if the temp drops below where it is set, and will shut the boiler off if the temperature equals or is greater than the setting on the clock. It will not heat up or cool down any faster by turning it fully up or down. It is designed to maintain the temperature that it is set to.

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To the last poster with the Immersion. Your boiler should be heating your Cylinder, not the Immersion heater. The Immersion heater is suitable as an emergency HW supply or some people find using the Immersion in the summer (when the heating is off) may be cheaper than using the gas to heat HW only.

Having said that, I have seen systems where the Heating is run from the (system)boiler, but the HW were run solely on Electricity ith a header tank. A whole Council estate in Southampton was plumbed in this way!

It is easy to check if this is the case, haave a look at your Cylinder, how many pipes come out of it, if there is only one at the top and one at the bottom (on the side) it is not connected to the boiler. If there are four pipes, with two additional ones coming out of the side half way up, then it is connected to the boiler.
You then need to check your programmer settings to make sure the gas is heating up the How water supply.

Even if both systems are heating the Cylinder, you won't be paying twice the cost, as both Immersion and Boiler will switch off once the temperature is met. However I wouldn't advise leaving the system running like this.