Central Heating Thermostat and TRV Settings Advice Needed

OK folks, long story and looking for some expert advice as my Central heating is driving me crazy

I have read several posts on the forum but none so far have answered by concern.

My house is 9 years old, boiler, tank and radiators all in very good condition. The house has three storeys with 2 large bedrooms in the roof space.

The whole house has generally been difficult to heat even with TRVs fully open with the top 2 bedrooms in particular very cold which I had put down to poor insulation (which has been remedied with additional loft and wall insulation) and the fact that each only has 1 smallish radiator positioned in the dorma window recess (not ideal). I keep the pressure in the expansion tank at around 1.8 bar therefore therefor I think there is enough pressure in the system to send hot water to the top storey.

I have toyed with the idea of installing either an additional radiator in each bedroom or replacing the existing radiators with larger ones positioned better in the room.

I believe the radiators are balanced.

That said, recently I have come to the conclusion that even with new, bigger radiators, the real issue is that the central heating is simply not sating on long enough for the radiators throughout the house to get to a reasonable temperature!

My current set up is I have:-
• A Potterton Suprima 60L Boiler
• A Honeywell Electronic Programmable Thermostat in the ground hallway usually set for 21C when programmed to switch on
• Every radiator in the house has a TRV with exception of the radiator in the hallway near the Thermostat (maybe not ideal)

With the help of some kind, expert souls in this forum, I learned that the likely reason that the Central Heating does not stay on long enough is that the boiler is switching off when the hallway reaches the 21C set by the thermostat and of course the rest of the house does not get a chance to heat up adequately.

I decided to take advice from the forum and set the Thermostat very high (30C) and set each TRV to mid-point. The result ... each room became tasty very quickly and I modified each TRV until each room was comfortable. So far so good!

Here is the problem, my ground floor hallway is stifling (24C+) because the radiator does not have a TRV and is obviously still getting fed hot water because the Thermostat hasn’t switched off the boiler.

I even went so far as to fully close the lockshields on the hall radiator to switch it off completely but after a while a Red Warning Light Flashed on the Potterton Boiler which I suspect must be due to me restricting the flow (?)

Any suggestions? I have thought about having a TRV installed on the Hallway radiator so that I can regulate the heat there easier or do I have to have at least one radiator without a TRV?

You need to open the TRVs more. At the mid point they will be shutting off their radiators when the room reaches about 18C yet the boiler will continue trying to satisfy the room thermostat yet with the hallway radiator shut off, which is the reason you don't have a TRV by the thermostat, it will never be satisfied yet with all the radiators shut it has nowhere to circulate. Open up the hallway rad, turn the thermostat to 21/22 and set the TRV's higher. Now adjust the TRVs to a point that makes each room comfortable.

Thank you ALCPlumbing for the quick response and advice.

However, what you suggest is the same as my original set up: hallway thermostat at 21C all room TRVs fully open however the boiler shutting off once the hallway reaches 21C and the bedrooms not heating up quickly enough and remaining cold whilst the hallway is kept nice.

When my kids come in from school there is no way to call for additional heat in their rooms because the boiler is not kicking in due to the hallway thermostat.

I was hoping that there was a way to reduce or slow down the heat buildup in the hallway so that rooms get a chance to heat up when needed. I don't want to do away with the room thermostat as I like the idea of having timed control.

I was planning to spend £100s on new, bigger radiators in the bedrooms but I don't see the point if hallway thermostat stops them from receiving long enough hot water feed.

Any other thoughts? Advice always appreciated.

r8r8r8r8 said:

The house has three storeys with 2 large bedrooms in the roof space.

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1. Is that as originally built, i.e the bedrooms in the roof space are the third floor?

2. Is the Potterton 60L the original boiler?

3. Check you heating requirement using the Baxi Boiler Calculator.

To take account of the rooms in the roof, I suggest you do it first as a two floor house and then as a three floor and take the average.

It might also be worth checking the total output of your rads. The Stelrad Catalogue, page 44 can be used, provided you don't have fancy "designer" rads, as the out put does not vary significantly between makes.

Hello and thank you D_Hailsham

The house has had no modifications since built. The two bedrooms have always been in the house and yes the Potterton 60L is the original boiler.

I used the Baxi Boiler Calculator and for a 3 storey house including the 2KWh for water heating suggested a minimum Boiler requirement of 13.5KWh. I checked a homeheatingguide and it suggested that the Potterton has an Output of 17.6KWh (I hope I am interpreting that right).

I haven't checked the radiators yet but they are all regular double or single radiators. As mentioned I don't think the existing radiators in the roof space are in a good position under the dorma window but please note, the concern with cold rooms is not only the 2 roof space bedrooms ... the first floor bedrooms are not great either.

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First easy thing to try is open the lockshield valves open the smallest amount you possibly can which still allows water to pass through on the hallway radiator. I've done that to mine and it just warms a little until the other TRV's start shutting down and more water is forced through (so it warms more and shuts off the room thermostat). It might be worth instead of upgrading the bedroom radiators to put a SMALLER radiator in the hallway or get an automatic bypass valve installed and have the hallway radiator shut completely (or with a TRV on low).

How far from the radiator is the room thermostat?
Should ideally be 1.2M from the floor, away from other heat sources, on an internall wall.

Armo74 said:

How far from the radiator is the room thermostat?
Should ideally be 1.2M from the floor, away from other heat sources, on an internall wall.

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Hello ... The thermostat is on an internal wall, 1.5m off the ground and 1.3m horizontally away from the radiator

St0rmer66 said:

First easy thing to try is open the lockshield valves open the smallest amount you possibly can which still allows water to pass through on the hallway radiator. I've done that to mine and it just warms a little until the other TRV's start shutting down and more water is forced through (so it warms more and shuts off the room thermostat). It might be worth instead of upgrading the bedroom radiators to put a SMALLER radiator in the hallway or get an automatic bypass valve installed and have the hallway radiator shut completely (or with a TRV on low).

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I'll try opening the lockshields as little as possible to see if that helps. I am not an engineer (hence seeking advice) but thinking about it rationally, the problem seems to be that the hallway is heating up far quicker than the bedrooms and shutting down the boiler. Anyway that I can slow down the heating up of the hallway would (I believe) go a way to solutioning BUT welcoming all the advice so far ... great help everyone.

r8r8r8r8 said:

I used the Baxi Boiler Calculator and for a 3 storey house including the 2KWh for water heating suggested a minimum Boiler requirement of 13.5KWh. I checked a homeheatingguide and it suggested that the Potterton has an Output of 17.6KWh (I hope I am interpreting that right).

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Yes the Potterton is 17.6kW, so it should be more than adequate for your house. There is also some spare capacity if you want larger rads on the top floor. However, bedrooms rads are sized for a temp of 18C, not 21C, which might explain why they feel cooler. Do you shut the doors or keep them open?

the concern with cold rooms is not only the 2 roof space bedrooms ... the first floor bedrooms are not great either

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Have you checked the rooms' temperatures with a thermometer?

If the rads are not giving off the correct amount of heat, setting the TRVs to max won't have any effect.

Although you believe the rads are balanced, I would not agree. Try following this procedure:

1. Remove all TRV heads and set rad wheel valves to max open (anticlockwise)

2. Close lockshield (LS) valves (clockwise) then open by one-third (1/3) of a turn.

3.Turn on boiler and set the heating temperature to approx 75C (that's with the pointer between 5 and 6.

4. Set the room thermostat to a high temperature so the heating doesn't keep going on and off.

5. Let everything heat up.

6. Check, by touch (or with a thermometer,) the temperature of the return pipe to the boiler. (That's the cooler pipe.) It should be about 65C.

7. If necessary adjust pump speed (lower speed = lower temperature)

The aim of balancing is to have the return temps for each rad the same. This is done by adjusting the LS valves. Open the LS to raise return; close LS to lower return. Adjustment should be made in very small steps, 1/10th of a turn or less.

8. Check the return pipe temperature of the all radiators.

9. Close very slightly the LS valve on the rad with highest return temp.

10. Wait 5 minutes.

This will affect the other rads, so you have to repeat 6 to 10 until the boiler return and rad returns all seem to be the same temperature.

Do not expect perfection, even if you are using a thermometer.

When all rads have been balanced, replace the TRV heads, set the boiler stat and room stat to the usual settings.

If you find that the room stat turns the boiler off before other rooms reach temperature, slightly close the LS valve on the hall rad. This will reduce the rad output so it will take longer for the hall to reach temperature.

Thank you D_Hailsam, I will give that a bash. Hopefully get a chance over the weekend or I may have to wait until I invest in a decent thermometer.

That's the great thing about this forum. People genuinely wanting and trying to help. Thanks everyone.

Just an update ... restricting the flow in the hallway radiator and opening the TRVs and Lockshields in the bedrooms is definitely improving the situation but worried that opening the lockshields in the bedrooms will be having an adverse effect on the balance of all the radiators.

I haven't had a chance to properly check the Radiator Balance. Can anyone suggest a good, reasonably priced thermometer for this? Bearing in mind that the pipework is plastic can I use the TRV inlet and Lockshield valves to test the drop in temperature?

Thanks again.

r8r8r8r8 said:

Can anyone suggest a good, reasonably priced thermometer for this? Bearing in mind that the pipework is plastic can I use the TRV inlet and Lockshield valves to test the drop in temperature?

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You can buy reasonably accurate Infrared thermometers for about £20.

You have to be careful using them or you will get false readings.

1. They average the temperature over an area. This called the spot distance ratio, e.g. 8:1. This means that if you are 8cm from the object, the spot will be 1 cm across. So you need to be close to the pipe to ensure you are not getting a false reading.

2. The material you are pointing it at affects the reading. So shiny new copper pipe will give a much lower reading than old oxidized pipe.

The chrome plated body of a valves may not be a good idea as it will under-read the temperature.

If you can feel the temperature in the plastic pipe, you should be able to use an IR thermometer to read the temperature of the pipe. Just make sure the temperature is what you would expect, particularly on the flow, which shouldn't be much different from the boiler reading. (There will be a slight drop due to heat losses in the pipework.)

You could wrap each pipe in some black insulating tape and measure the temperature from the tape.