How exactly does a gas boiler work?

ally18

Yes, when the new boiler was put in, I had these fitted to all the radiators (bar the hall one) in the house. They are set on the highest setting as advised by my plumber.

Fruit_and_Nut_Case

ally18 wrote: »

Yes, when the new boiler was put in, I had these fitted to all the radiators (bar the hall one) in the house. They are set on the highest setting as advised by my plumber.

Having them all on the highest setting seems to negate the reason for having them.

I don't know the recommended setting procedure but I adjusted mine to give the individual room temperatures I wanted; cooler in bedrooms, comfortable in reception rooms and toasty in bathrooms.

oldskoo1

I have a big drafty hall with the only radiator the opposite side. Stat was set to 18c but we found all the rads and rooms reached temperature much quicker than the hall. This resulted in the boiler short cycling and running another 30 mins or so to raise the hall temp. If it was maintaining temp it wasn't so bad.

You won't have the short cycling problem as you have a modern modulating boiler. My point is if all is working ok the stat temperature in the hall might need lowering if as you say all the rooms are warm but the hall is still demanding heat.

I have 19 radiators and all of them apart from 7 on the ground floor have trvs. They all get warm within 30 mins to 45mins. Having an old style boiler I adjust the water temperature manually. Currently set to 65c but in the cold of winter it will be at max. If the boiler is correctly rated to your radiator requirements it should only take this amount of time. However it could take longer if you don't have trvs or your radiators aren't balanced.

Im assuming he installed a boiler powerful enough to drive your radiators? Do you have trvs fitted which will shut off the radiators when they are at temp to direct the hot water elsewhere? If you don't it could take a bit longer to heat up. Have you therefore balanced your radiators? Do all get warm evenly? If the last few in the loop are cool but the first ones burning hot this is going to create problems trying to raise the temperature.

It is best to have the stat in the coldest place really but set the temperature accordingly. I figured mine in the hall was simply too high at 18c, all the rooms were at 19-21c as per the trvs long before the hall stat turned off. Make sure the radiator in the hall is wide open and getting the full heat. I ended up putting it at 16.5c and still all rooms hit their temp before the hall.

oldskoo1

I see you replied about the trvs whilst I was typing

Trvs as mentioned by someone else at max is not right. I'm confused why he would suggest that, your installer.

You need to set them to 2 to 2.5 (18-19c) in he bedrooms, frost setting or 1 in unused rooms and 3 to 3.5 (20-22c) in living spaces and bathrooms. Go up half a point or a point on these if you are 60+

These settings to distribute heat much better.

Before you change this, I would turn on your heating and check the radiator balancing. The radiator nearest the boiler (not necessarily physically!) will heat up first, check all radiators in the loop get even heat. Have a look for radiator balancing guides in YouTube or the wider internet. It's worth doing if you find some radiators are cool to touch and others boiling hot. It takes a bit of time but it's worth it!

To give an example like you our sitting room was always freezing, we thought it was because it was north facing and never got sun. That is true to an extent it's nice to go in there in summer however in winter it was too cold. After balancing the radiators it got noticeably warmer in there, it made a huge difference. Took a few hours or balancing by hand but I managed it.

ally18

I didn't know that about the trvs as the plumber never mentioned what the equivalent temps were for each setting. He just said to leave them on 6 so they heated up quicker, that way the boiler would not be on for so long? He said they heat up quicker at the higher temp?

All the radiators, once heated, do feel the same, they are very hot. I kept checking them when I had the boiler on but this has only been twice so far. The radiators were never this hot from the old boiler . I have 7 radiators in total, one is a towel radiator in the bathroom that does not have a trv.

I have the thermostat set at 18.5 at the moment so when I get home, I will lower it and depending on the temp, I will switch the boiler on.

I will turn the trvs downs tonight to what you have advised and then monitor the time.

The trvs, as far as I am aware, don't switch off automatically once the temp is reached.

Thank you very much for the advice.

DragonQ

The whole point of TRVs is that you can heat different rooms to different temperatures, which is generally more efficient. The room you want warmest should be on maximum (living room usually), then the others at whatever relative setting you want (maybe 4 in bathrooms, 2-3 in bedrooms and hallways).

It helps if you have your thermostat in the room with the highest TRV value but it doesn't matter too much because you can just adjust it manually (e.g. if it's in the hallway, you might have to set it to 18 °C to get 20 °C in the living room).

You're correct that the TRVs won't ever turn off the boiler - that's the job of the main thermostat.

oldskoo1

That is quite confusing advice your plumber gave you.

TRVs are automatic shut off valves once the desired temperature has been reached. If you set them on 3 which is roughly 21c as the TRV detects the air temperature is 21c or close to it, it gradually shuts off the valve on that radiator.

What this does is direct hot water from the boiler elsewhere which should lead to a quicker warm up time (providing the TRVs are set correctly).

Him advising you to keep it at 6 seems a bit odd, rooms would get hotter than they need which is essentially waste heat which could be pumped into large rooms like your living room. So it will make them heat up very hot but not necessarily quicker.

What you find with modern boilers and correctly set TRVs is as the first few radiators of your 7 shut off, the reaming few get hotter water from the boiler and this should speed up warm up time. As the boiler is usually specced to service around 7 radiators it will modulate the gas flame down and use less gas if the TRVs have turned off a few radiators, old boilers just had an on/off thermostat. If you had all TRVs open its still going at full pelt (hypothetically) until your hall stat is satisfied. That isnt really the idea with modern modulating, pump regulating boilers.

It's interesting you said all rads feel the same once heated, ideally with correct balancing and TRV settings they should be fairly even within the first 5 mins.

It is good your new boiler is supplying sufficient heat now so you are on the right path.

On the last point the TRVs should switch off automatically, you wont notice a visual change i.e. they wont go from 2.5 to 0 on their own, i just meant they control the flow of water automatically, by shutting off that radiator once the temp is reached which diverts the hot water elsewhere.

Radiators job is to radiate heat as the cooler air passes over the surface. The heat will be lost by the first radiators in the loop and by the last few it will be slightly cooler. If you TRVs shut these radiators off and you have a well balanced system then you get a more even heat distribution and theoretically a faster warm up time.

I feel like i have explained what i needed to in a roundabout way but hopefully it makes sense.

ally18

Thank you so much for your replies, esp oldskoo1, you have explained quite a bit. Right to describe lastnight -

When I got home, I turned all the trvs down to what was recommended, 2.5 in the bedrooms and 3.5 in the living room and dining room. I also turned the thermostat down to 17. It was showing 15 as the temp at this time, which was 7.40pm.

So, boiler was put on to the timer which was planned to turn off at 10pm. After 10 mins the radiators started to get hot all through the house and I checked on the thermostat after30 mins, it had increased to 15.5 and then at 8.45 it was 16d.

Right, then at about 9.10 the radiator in the lounge clicked, I didn’t think anything of it at the time but then I realised it had switched off! I started thinking the boiler had switched off but no it was still running, the thermostat was saying 16.5d and the hall and bathroom radiators were red hot. Plus all the other trvs had switched off too. (Sorry for being thick, but I didn’t know they worked like this! It’s obvious to me now, doh!)

I tried increasing the trvs by a number and of course they switched back on until the boiler then went off through the timer. But at 10pm the thermostat in the hall remained at 16.5, that was after being on for 2 hrs 20 mins. It didn’t even reach the set temp of 17d in that time so I assume this was because of the lowered temps in the lounge and dining room?

So, let me just get this right, when the rooms with trvs get to the temp on the trv, they will turn off but if the thermostat in the hall has not reached the set temp, the boiler will continue to run until this is reached? Meanwhile,the trv radiators will switch back on if the temp in that room then falls?

Doesn’t this mean that they could be switching on and off all the time? Is that why the plumber said to keep the trvs to 6 so this doesn’t happen?

Or am I getting confused now. I just want the boiler to run as efficiently and as cheaply as possible for obvious reasons. Really sorry for the long post and questions.

jrawle

daveyjp wrote: »

55 for water is also quite high. You are heating water to a temp where cold water is needed to cool it down, thereby wasting energy.

No! 55°C is the temperature required to kill bacteria such as Legionella and other nasty things that can live in hot water. That's why it must be no lower than this.

ally18

I finally have it worked out, I think.:) My hall area is going to cause a problem but I will use the trvs from now on to control the temps in the rooms.

Thanks very much everyone for the replies.