Best settings for room thermostat, TRVs and boiler stat?

[mjpg]

Hello, first post here - about our central heating controls - checked other posts here, and got some ideas, but hope others can give a bit more advice.

We have a 1920s 3-bed older house, mostly single-glazed, and although not very cold, can take a bit to heat up.

We've had all the TRVs replaced, as the previous were all stuck and we now have pretty good control of each rad.

Our problem is getting the house to warm up evenly - we've adjusted the TRVs carefully, but still end up switching them up to get some rooms to temperature, or down, because they seem too hot.

I'm wondering if the boiler, room and TRV settings are fighting each other. Or if leaving room doors open (as we often do) is causing issues.

Here's what we have:

* Ideal Mexico Super CF80 old gas boiler. Boiler stat set to 2.5.
* 4 radiators downstairs all with new Drayton TRV4s
* An old Drayton analogue room stat on the wall between the through-lounge - about 5-foot up wall. It's set to 19 degrees.
* 6 rads upstairs. One small one in the bathroom has no TRV.
* The hot water tank upstairs has a Danfoss RAVI thermostat set to minimum.
* Rads are vented, boiler serviced.
* Some TRVs are not in great places - but we are stuck with that.

Any suggestions as to where to start setting the various thermostats - or whether we should avoid using some - or swapping the old room stat? Or might we need to re-balance the rads?

Thanks in advance for any help.

 

[D_Hailsham]

Our problem is getting the house to warm up evenly - we've adjusted the TRVs carefully, but still end up switching them up to get some rooms to temperature, or down, because they seem too hot.

Provided the radiators are the correct size for the room, the normal reason for you problem is incorrect balancing of the system. See How to balance a CH system

Ideal Mexico Super CF80 old gas boiler. Boiler stat set to 2.5.

Set the boiler stat to max, the house will heat up faster. The wall stat has overall control over when the boiler turns on/off

Radiators downstairs all with new Drayton TRV4s
An old Drayton analogue room stat on the wall between the through-lounge - about 5-foot up wall. It's set to 19 degrees.

Why is the room stat set so low?

Changing the stat for a modern digital version, e g Honeywell DT90E, DT92E or the programmable versions CM901/907/921/927. They will give better control over the room temperature.

What setting do you have on the TRV4s?

Do the rads in the through lounge have TRVs?

6 rads upstairs. One small one in the bathroom has no TRV.

What setting do you have on the TRVs?

The hot water tank upstairs has a Danfoss RAVI thermostat set to minimum.

It should be set to 60°C. The reason for this is to prevent the growth of Legionella bacteria in the water.

Some TRVs are not in great places - but we are stuck with that.

Installing the TRV so the control is horizontal may help.

It is essential that the room stat does not shut the boiler off until all the rooms with TRVs have reached temperature, so the TRV is operating. This means the room stat should either be in the warmest room or in the one which takes longest to reach temperature.

 

[Alfredo]

The first thing I'd suggest is to open all TRVs to full, room stat full up then adjust your boiler stat to a position where all rads get hot, without being outrageosly hot. Your mexico has a big old cast iron Heat Exchanger that requires quite a heat input to get heat out. Turn the boiler stat down to the lowest setting at which you are still happy with the rad temp..too far and they will just go cold. At this stage you know you are putting enough heat into the system to heat the house.

Then with room stat still right up, adjust TRVs to mid point..or whatever point represents 20-21c. In rooms you don't use, turn them down, but not completely off(unless you keep the doors shut). A cold room will get mould, and will rob a hot room , so always have some heat on in unused rooms, just to keep them aired. If your living room is big and radiator marginal in size you may need to turn TRV up

Then your room stat. 20c=68f= nice spring day..so most have it on 21c. However if you are all stuck in front of telly, 21 might seem cool. On the other hand if you have been active 21 might seem hot, so adjust to suit. Cylinder stat..never less than 55c, never more than 60c. (I see you have a tapstat on the cylinder.....never yet got one working quite right, but you should be able to turn it gradually down from max to have water hot enough and not scalding) Jacket on cylinder..I trust..

Make sure your house is properly insulated. Lots of cheap deals available from your power supplier. Thats the cheapest way to save dosh and stay cosy.

Alfredo

 

[mjpg]

Thanks D_Hailsham and Alfredo for such a quick and helpful response -

ANSWERS

1. Room stat set low at 19C - as we thought that would be warm enough - perhaps not. We'll try higher.

2. TRV4s downstairs are set at
4 in kitchen diner
4 in middle room
5 in front room
2 in downstairs hall

Upstairs they are all about 3.

3. Yes - rads in the through lounge have TRVs

4. Hot water cyclinder - I thought we might save some energy there (seems I took a risk!) since we use little hot water as we use electric shower and dishwasher and heating the tank seemed a waste (it is not pumped so it heats anyhow). It is lagged (sprayed on foam). I will turn it up.

MORE INFO

I will try what you suggest to check the boiler stat setting, but I think the boiler can do pretty well in heating the rads as the lounge one can get far too hot to touch.

Before we had the TRVs, the house could eaily get too hot - so I think it is all capable.

QUESTIONS

Is balancing a DIY job? Seems straightforward, providing I can guess the pipe-run correctly. Are there any gotchas?

Do we remove the TRVs in the through-lounge?

I'm not clear if boiler stat to max or lower is best option from what you've both said.

Thanks again

 

[Servotech]

Hi mjpg,
You can DIY balance your ch system quite easily yourself by using this method.
Turn off all lockshield valves.
Fully open all TRVs.
Switch on boiler (ch) all rads must be cold at this point.
crack open all lockshields by no more than 1/4 turn.
After 15mins check all the rads by touch, some will feel colder than the others on these you need to open the lockshield another 1/4 turn.
Again after another 15mins go round all the rads and if some are still cooler than the others open these by another 1/4 turn.
Carry on until all the rads are the same even temperature and when this is achieved, hey presto you have balanced the system.
This is an easy fool proof method which I actually prefer to messing about with clip ons thermometers.

The running of the boiler thermostat on max is the modern method of thinking, but if you want to run it on a lower setting I can't see a problem with this.
No TRV in the bathroom is a good idea methinks especially if you like a nice warm towels after a bath/shower.

 

[D_Hailsham]

Room stat set low at 19C - as we thought that would be warm enough - perhaps not. We'll try higher.

Probably a bit on the low side for most people - 21C is the norm.

TRV4s downstairs are set at
4 in kitchen diner
4 in middle room
5 in front room
2 in downstairs hall
Upstairs they are all about 3.

The problem is that, with the stat set to 19C, rooms with TRVs set to 4 and 5 will not reach temperature before the boiler goes out.

rads in the through lounge have TRVs

The wall thermostat need to be in control, not the TRV, If you set the wall stat to 19C and the TRV to 4 (about 21) the room will never reach the TRV temperature. If you set the wall stat to 21C and the TRV to 3 (about 18C, the room will never reach 21C, so the boiler will run continuously.

Three options:

Remove the heads from both TRVs
Set them both to max
Change them for wheel valves

You could also try doing the above only to the rad furthest from the wall stat. Set the other to the required temperature (4)

Hot water cylinder - ... it is not pumped so it heats anyhow.

Hold on a sec before you turn the stat up. You obviously have a gravity circulation HW system.

Is there a motorized valve in one of the pipes going into the side of the cylinder?

Is balancing a DIY job? Seems straightforward, providing I can guess the pipe-run correctly. Are there any gotchas?

Yes.

Getting the runs are not essential, but it helps. You can often guess them as they are normally fairly logical and take the shortest route between two rads. You can also check by feeling the flow pipe as they heat up from cold - more than one person is useful here.

Having the same difference across each rad and the boiler is more important than the actual temperature.

You need to make sure the wall stat does not turn the boiler on and off while balancing.

I'm not clear if boiler stat to max or lower is best option from what you've both said.

The temperature set on the boiler stat is the maximum it can reach. This will normally only occur while the house is heating up from cold. After this the boiler is turned on and off by the wall thermostat and may not reach the boiler stat temperature while it is on. This will depend on the rate at which the house looses heat and the outside temperature.

Try MAX to begin with; then turn it down a bit every few days and note the effect.

 

[Alfredo]

If rads are too hot to touch boiler stat is too high...or broken. I've been in enough houses where the boiler stat is on so high the occupants cook as the radiators almost glow, then turn off the heating, then freeze, then turn it on again, then cook etc etc. Its crazy and wastes masses, and its dangerous for kids (well everyone really) as they can cause serious burns.

Get the rads to a nice hot steady temp you can just touch without going OUCH

If you don't use the HW cylinder its not compulsory to have the tapstat on at all.

Alfredo

 

[ajrobb]

Speaking as a novice:

With a non-condensing boiler, there is not much to be gained by turning it down below 65°C. This boiler temperature should still be able to heat the water cylinder to a legionella-killing 60°C (at least after an hour at that temperature). Unfortunately, 60°C is also hot enough to cause 3rd-degree burns and about 60 (very old and very young) people a year die in the UK from immersion in hot water. (Bath taps can be fitted with temperature limiters.)

I'd go with Servotech's radiator balancing strategy. If all your lockshield valves are currently completely open, you might find that you can run your pump on a lower setting too; after balancing, if most of the radiators have significant flow noise, you might need to turn your pump down and continue balancing.

 

[mjpg]

Thanks everyone. Very impressed by the response.

I'm going to take a good look tomorrow and try some of this.

One or two questions (mainly about the VERY hot rad) - but I'll post again tomorrow.

Thanks.

 

[mjpg]

This is just about the hot water cyclinder for now

The cylinder is small, with an imersion heater.

There is no valve or pump with the cylinder. There is only one pump on the whole heating system (a Myson Unit three) and it is downstairs next to the boiler. So I assumed that the hot water is not pumped.

I'd thought that as we don't use hot water much, that it was wasteful to heat the tank - that's why I turned the tank thermostat right down. I did not know about the legionella risk.

QUESTION

Do I need to let the tank get to 60 degrees C or not? If so, do I just remove the tank stat?

 

[D_Hailsham]

The cylinder is small, with an immersion heater.

There is no valve or pump with the cylinder. There is only one pump on the whole heating system (a Myson Unit three) and it is downstairs next to the boiler. So I assumed that the hot water is not pumped.

Are you saying that the immersion heater is the only way of heating the cylinder? Or are there pipes connected to the side of the cylinder, one in the middle and one below it, which do not have any valve etc on them?

If the latter, then the hot water temperature will be controlled by the boiler temperature.

How many pipes are there connected to the boiler (ignore the gas pipe)?

Do I need to let the tank get to 60 degrees C or not? If so, do I just remove the tank stat?

60c - YES

Do you mean the immersion heater stat or another stat? If the immersion stat, then this should be adjustable to give the required 60C. If another stat, what is it and where is it located?

 

[mjpg]

HOT WATER TANK
This is both immersion and from boiler. I think all questions about this are sorted and I need to set the tank stat to around 60 degrees.

BOILER PIPES QUESTION
Apart from the gas (which is at the lowest point I think) there are four pipes at the back of the boiler - two on the right which seem to go upstairs and two on the left, one of which goes straight to the pump.

 

[D_Hailsham]

BOILER PIPES QUESTION
Apart from the gas (which is at the lowest point I think) there are four pipes at the back of the boiler - two on the right which seem to go upstairs and two on the left, one of which goes straight to the pump.

OK You must have a pumped heating, gravity hot water system.

As there is no valve on the circuit to the hot water cylinder, the temperature of the water in the cylinder will be determined by the setting of the boiler thermostat.

I take it that there is no thermostat fixed to the side of the HW cylinder about half way up.

I also assume that the timer allows hot water only in the summer but heating and hot water in the winter.

Can you post a pic of the HW cylinder and the pipes connected to it? A general view is better than closes ups.

 

[mjpg]

D_Hailsham - I fear I am confusing you.

The cylinder DOES have a tank stat. The sensor is about 1/3rd way up the tank. The stat (a RAVI) is on the exchanger inlet.

The tank has four pipes - a water inlet at the bottom, and outlet at the top. And an exchanger (I assume) in and out in the bottom third (two pipes).

 

[D_Hailsham]

D_Hailsham - I fear I am confusing you.

The cylinder DOES have a tank stat. The sensor is about 1/3rd way up the tank. The stat (a RAVI) is on the exchanger inlet.

I had forgotten about that, you had mentioned it in an earlier post. It's a thermo-mechanical device, a bit like a TRV, which shuts off the circulation though the coil when the cylinder is up to temperature. That's better than no control at all, but it does mean that the boiler can carry on running even when the cylinder is up to temperature.

It also means that you do not have completely independent control over the CH and HW times.

The cheapest way of achieving this is by replacing the RAVI with a motorized valve and a thermostat attached to the cylinder. It's called a C Plan system.

The more expensive way is to convert to pumped HW, but that means major alterations to the piping.