TRVs versus Room Thermostat

[wbjimmy]

Ive recently replaced all my radiator valves with TRVs and installed an automatic by-pass valve in my airing cupboard. My plumber has told me I needn't remove the old room thermostat (mounted in the hall) but merely set it to maximum so that it doesnt override the TRVs - including the one in the hall. I have also retained my combined CH and HW programmer (linked to a 3 way valve) which switches off the boiler overnight. My question is whether this is the most economical way of using my TRVs or whether I should remove the room thermostat.
Also, can someone please explain why, when the TRVs are shut off, it is still more economical to have hot water circulating all day through a by-pass valve in an un-thermostatically controlled airing cupboard than a non-TRV system which just turns off the boiler when the room thermostat reaches the required temperature?

 

[Slugbabydotcom]

I would suggest you just set the roomstat either the same or a few degrees higher than you want the room temp to be and use the TRV to be the main temp control for that room.

You are correct by implying that if something is switched off it uses no energy.
The problem is that the room with the stat in could have shut down the heating before other rooms have reached the required temperature.
The risk of having a cold room is inversely proportional to how high the room stat is set.

Trial and error will help you achieve a comfortable and efficient setting

 

[Dan Robinson]

OP - your plumber is an idiot.

Slug, you have it wrong also.

if you don't want to remove he head of the valve nearest the room stat then set that valve to max and the roomstat to where you want it.

It is not more efficient to have the boiler pumping hot water around the bypass with the rads tuned off.

 

[Slugbabydotcom]

I don't think I have it wrong but do admit I may have went a bit too deep.
Removing the TRV head or simply setting it to max in the room with the thermostat is probably the best idea as the risk of having one or more rooms not reaching their set temp is minimal if the rads are sized properly and the issue I was considering is of little consequence.

 

[Dan Robinson]

Apologies.... i misread your post.....


But the OP's plumber is still an idiot

 

[doitall]

But the OP's plumber is still an idiot

2nd that if he/she is a plumber,

 

[SimonH2]

It can be made to work - but it involved more plumbing and expense (not to mention the arguments that will no doubt happen as to whether it's efficient ).

Fit a buffer tank between boiler and CH (with a pump if it's not included in teh boiler), control the boiler on stats (high-low) on the buffer tank, and fit a modulating pump on the CH. The TRVs can then do their job and control the temp in each room, with the modulating pump " "backing off" the pressure and flow as the TRVs shut down. The stats on the buffer tank will turn the boiler off when there is stored heat in the buffer. Supply both boiler and CH pump from the programmer.

Or do as the others suggested, make sure the TRV in the room with the stat cannot control the room below the operating point of the stat - so the stat can turn the boiler off when the room is warm.

 

[wbjimmy]

Thanks for all the advice. It seems The cheapest, and possibly the easiest, way ahead is to set the room thermostat a couple of degrees higher than the TRV in the same room and if I find the boiler is shutting off prematurely ( i.e. before the other rooms have reached their desired temp) I can raise the room thermostat setting by an additional degree or two.

 

[doitall]

No, if the TTRVs shut off first the room stat will never work.

The room stat conrols the temperature and provides an interlock for the boiler to save it cycling on/off all day.

Get rid of the TRVs in the room with the stat, (ideally the lounge.)

 

[ALEC1]

Also, can someone please explain why, when the TRVs are shut off, it is still more economical to have hot water circulating all day through a by-pass valve in an un-thermostatically controlled airing cupboard than a non-TRV system which just turns off the boiler when the room thermostat reaches the required temperature?

Its not more economical. Compensation, modulating, or Opentherm controls, which are desigened to work with condening boilers, run the boiler at a progressively lower flow temperature as room temperature rises.

You don't say what boiler you have, but if its a vaillant you may be able to retrofit one'

 

[wbjimmy]

Gosh I'm beginning to wonder whether it was worth fitting the TRVs in the first place! The room stat is currently situated in the hall and is hard wired to the programmer in the upstairs airing cupboard and a conventional wall hung Valliant boiler in the garage.
Shouldn't I just disconnect the room stat because it will always interfere with TRV on the hall and if so, how do I do this without mucking up the programmer?
Should I just accept that with a TRV-enabled system you must always have some hot water circulating round a by-pass loop ( either a valve like mine or at least one rad) when the TRVs are closed and that this is still more potentially economical than heating the whole house to the same temp with a single room stat?

 

[doitall]

I've no idea what you have but it sounds a right mess.

The room stat is number 1 as it controls the boiler in the heating mode, save you money in other words by turning the boiler on/off.

The TRVs control all the room temperatures except the one with the room stat.

The cylylinder should control the boiler and pump in hot water only mode.

The by-pass should be an auto by-pas valve and closed more than open.

Perhaps a bit more info and a drawing showing how it's all been chuck in.

 

[Charnwood]

No heating system should be all-TRV-no-room-stat, even with a bypass valve. It is not efficient. It is costly to run, relatively.

People have suggested that you lose the TRV in the room with the room stat, but you persist in wanting to do the opposite - remove room stat and keep the inefficient all-TRV/bypass method. If the room stat never triggers, the boiler will fire-up 24/7 because the temperature the room stat is set at will never be attained.

Room stat should ideally be in the room you want to be the warmest. That room should have no TRV. All other TRVs will be allowed to attain the heat required for their specific rooms and cut off before the boiler is shut down by the room stat. Efficiency personified.

 

[wbjimmy]

OK. Here goes.... I have a 4 bed house, kids have recently left home (so 3 bedrooms are rarely used) , and a wife who always wants to turn up the heat in the lounge in the evening! So I decided to convert my CH system by installing TRVs on all my rads and thereby let my wife turn up the heat in the lounge when she felt cold without heating up the rest of the house. My system comprises a Valliant non-condensing system boiler, a Drayton 7 day hot water/ CH programmer and a three way valve in the airing cupboard, and a hard wired Drayton room thermostat in the hall. As my rads all had twin entry microbore valves I got a plumber to replace them with Drayton bidirectional TRV4s and new Peglar lockshield valves. My plumber also installed a Danfloss automatic bypass valve in the airing cupboard which he said would be more efficient than merely not fitting a TRV to one of my rads (say in the bathroom).
He also advised me to keep the existing room thermostat turned up high (or even max) to avoid it conflicting with the hall rad TRV. but this suggests the boiler is almost constantly running when the programmer is on. So I wanted to know whether there was a more efficient way of setting up my new TRV-adapted system which would allow my wife to turn up the heat in the lounge when she wanted it without having to heat up the rest of the house or have the boiler running all the time.
p.s. I have suggested she puts on a pullover or fleece but she wasn't amused!

 

[doitall]

What you should do.

Assuming the by-pass is on the heating side of the 3 port valve is buy another or move the existing stat to the lounge and remove the TRV from that room.

Then you can disable the room stat in the hall.