Temperature controls

[Harry Singh]

I have a thermostat in the hall that signals the boiler to switch off when the temp reaches 19 degrees.

There is also a thermostat on the bolier 1-6 and max. And on the individual rads I-V.

If I want to leave the hall thermostat alone is there anyway I can set the boiler and rad controls to put the least strain on the bolier?

I'm concerned about the bolier running at high pressure, and that's due to be looked at - it might be an EV issue - but if there's a sudden drop in temps I'm wondering how to avoid running my bolier for too long and letting it get "a head of steam" without compromising the hall thermostat.

 

[stem]

To get the best from your heating, you need to understand how the thermostats work in relation to each other.

The room thermostat is provided as a boiler interlock and will switch the entire central heating off when the set temperature is reached in your hall, and then back on again when it falls below the set temperature. Most folks choose a setting that is comfortable for them, usually somewhere between 18 to 21 degrees C. Once you have found a comfortable setting then it can be left alone to do it's job.

TRV's control only the individual room temperature in which they are located. They do this by gradually reducing the flow of water to the radiator as the set temperature is approached. Again, once a comfortable temperature is found they can be left alone and will adjust the flow of water automatically to maintain the set room temperature.

The boiler thermostat selects the temperature of the water leaving the boiler, so effectively selects how hot the radiators get. Condensing boilers are more efficient with cooler return water, so with them, it can be beneficial to set the boiler at the lowest temperature you can but at which your house still heats up fast enough. This will change as the weather gets colder and when more heat is needed to get your home up to the required temperature. Some boilers provide suggested settings in the manual. Here's an example from Vaillant.

If your boiler isn't a combi, and it also heats stored hot water, the boiler thermostat setting should be at least 10 degrees above the hot water temperature setting on the cylinder thermostat, otherwise it will never reach the set temperature and the boiler will cycle continually.

 

[Harry Singh]

Thanks for that. It seems the key is the hall stat as it controlds the boiler when the boiler is in an active period. So the quicker the hall heats up the quicker the stat switched the boiler off. It suggests to me that at least the hall rad needs to be wide open and maybe the boiler a little higher so the rad heats up quicker.

 

[JohnD]

Thanks for that. It seems the key is the hall stat as it controlds the boiler when the boiler is in an active period. So the quicker the hall heats up the quicker the stat switched the boiler off. It suggests to me that at least the hall rad needs to be wide open and maybe the boiler a little higher so the rad heats up quicker.

do you mean that the hall heats up slower than the other rooms?

It's supposed to.

What are you trying to gain?

 

[stem]

It seems the key is the hall stat as it controlds the boiler when the boiler is in an active period.

Yes, that's the idea.

The quicker the hall heats up the quicker the stat switched the boiler off.

Also correct.

It suggests to me that at least the hall rad needs to be wide open and maybe the boiler a little higher so the rad heats up quicker.

Generally true, but sometimes is can be reduced as part of balancing the system . Occasionally if the hall warms up too quickly and so turns the entire heating off before the other rooms have got warm, the hall radiator can be closed down slightly. In any case, there certainly shouldn't be a TRV on the radiator in the hall where the room thermostat is located, otherwise it can interfere with the correct operation of the room thermostat.

 

[JohnD]

put the least strain on the bolier

The boiler is not "strained" by being used.

Do you mean "to achieve best efficiency in use of gas?"

 

[fixitflav]

It suggests to me that at least the hall rad needs to be wide open and maybe the boiler a little higher so the rad heats up quicker.

I depends on the size of the hall rad relative to the heat demand. If the rad is too big the system will switch off on the room stat before all the other rooms have reached their TRV setting. In that case you might need to throttle the hall rad.

 

[Harry Singh]

The boiler is not "strained" by being used.

Do you mean "to achieve best efficiency in use of gas?"

We have our bolier in the on mode for two hours in the evening. I'm trying to figure optimal settings so that in that period it's actually firing for the least amount of time to maintain the temperature at the level set on the hall thermostat. So yes that may wll lead to reduced gas usage.

 

[JohnD]

Assuming you don't spend much of your time in the hall, you'd do better to wangle the settings so your living rooms are at the desired temperature. As the other rooms warm up, their TRVs will close, and this will tend to increase the flow in the hall radiator. You only want the room stat to turn off the boiler when all the other rooms are warm. As the weather turns colder you may find that two hours on the timer is insufficient.

 

[Hot&Cold]

- it might be an EV issue -

are there any symptoms to spill re the mentioned item ?

 

[Harry Singh]

are there any symptoms to spill re the mentioned item ?

Boiler pressure dial was at 0. Let the water in to 1 bar. Run the boiler. Rose to 3+ bar. PRV valve opens. Switch off and it cools to 0 bar.

I tried to re-pressurise the EV and I have it at 1 bar consistenly in off/cool state. But it jumps to 3 bar after 45 mins. I suspect it will go 3+ after a bit longer and lose all the pressure but haven't let it go that far yet and it's been quite warm.

As I did the final re-charge with the stop-cock closed and the system sealed the theory (on another thread) is the EV is sound but I didn't expel all the water when I re-pressurised.

 

[RobTi]

but I didn't expel all the water when I re-pressurised

What do you mean by this statement, there should be no water in the ev, so nothing but air coming out the shraeder valve

 

[Harry Singh]

I thought the EV was a vessel with a diaphragm separating the air from the water side. Might have read dem dar threads all wrong though.

 

[flameport]

I thought the EV was a vessel with a diaphragm separating the air from the water side.

It is - assuming it's not busted.

If there is no air in it then it can be recharged, but only with the system pressure at zero and at least one valve open, so that as air is added, the water displaced can go somewhere.

If the EV has failed, then a new one is required.
Continually refilling the system with fresh water will quickly result in massive corrosion and very expensive damage.

 

[Harry Singh]

Yep - didn't have a valve open so I think I only did half (or less) a job. It doesn't rise as quickly as it did but it still heads towards 3+ bar eventually. Fortunately it's been warm so it's stable until a cold snap I guess.