Setting thermostatic radiator valves

QrizB

quartzz said:

"The TRV head (usually the knob bit) has a mechanism inside it that expands/contracts with temperature" - ah, so it's a sort of mechanical temperature sensor? (like a bi metallic strip or something?)

I've always imagined it as a wax capsule, but yes that sort of thing.

quartzz said:

.....is there any disadvantage to having the "reference" temperature as the TRV on 5, rather than 4? so the TRV is on maximum, rather than "not using" the capacity between 4 and 5?

A bit like Spinal Tap and their amps that go up to eleven?

Lorian

If you put your trv on 5 it's the same as not having a TRV - see my post above.

Please don't use pliers on the trv it's easy to damage it and it will leak. You need to be pressing it to free it up. Plenty of videos of people doing it on YouTube 

TRV are traditionally based on melting wax but some newer models are gas filled and act slightly quicker.

quartzz

Lorian said:

If you put your trv on 5 it's the same as not having a TRV - see my post above.

Please don't use pliers on the trv it's easy to damage it and it will leak. You need to be pressing it to free it up. Plenty of videos of people doing it on YouTube 

this is something I hadn't considered, but should have considered. I've actually already sprayed some WD40 or grease on it, but it hadn't made any difference. this property was empty for a few weeks before I moved in (October), the kitchen TRV has never worked while I've been here, so the TRV might have got stuck or something. can they get "un stuck"?

quartzz

QrizB said:

quartzz said:

"The TRV head (usually the knob bit) has a mechanism inside it that expands/contracts with temperature" - ah, so it's a sort of mechanical temperature sensor? (like a bi metallic strip or something?)

I've always imagined it as a wax capsule, but yes that sort of thing.

quartzz said:

.....is there any disadvantage to having the "reference" temperature as the TRV on 5, rather than 4? so the TRV is on maximum, rather than "not using" the capacity between 4 and 5?

A bit like Spinal Tap and their amps that go up to eleven?

er.....probably

Scot_39

quartzz said:

thermostat is in the hallway (the rads are only in rooms, with none in the hallways). so (and I'm guessing here) is it more efficient in terms of boiler heating element/motor pump/heating oil, to have the "reference" temperature in occupied rooms as TRV on 5, and to lower the other TRV's to for example 3.5

this is rather than, the current tactic of having the TRV's in occupied rooms at 3.5 to 4. being that I have just realised, that if my "maximum" TRV is set to 4, that actually means I'm wasting some boiler efficiency because I'm not using "20%" (in inverted commas) of the boiler output?

You are missing the crucial point about the TRVs - they have minimal impact until they cut flow to the individual radiator - when the room - or at least the room at the TRV point - reaches the set temperature (probably slightly above due to TRV hysterisis).  

At that point the boiler will need to deliver less power (energy over time) as no longer heating that one space - but can still deliver full flow to other rooms.

The master thermostat cuts the boiler - feeding all radiators at the point it's setpoint reached.

If the main thermostat cuts the boiler in the simplest system - you get no fresh hot heat flow to any of the radiators.  Which can lead to issues if radiators aren't well balanced against room losses.

There is no direct link between controls - unless you have the very latest smart TRV and thermostats - which are more predictive and actively also control boiler power modulation to increase room temperature accuracy.  

If because of main thermostat setting - it never cuts the main boiler flow - your TRVs regulate the individual spaces.

[Unless radiator power limits do first (the power is a direct function of temperature difference - so many quote effective power in kW or BTU at delta T 50 - so 70c flow for 20c room temperature).]

And so the reality is that what you need therefore also often depends on air circulation - as if heat one room higher than others - then that heat spreads to some extent - unless block it - e.g. close doors - see example below.

Have a read of

https://www.britishgas.co.uk/heating/guides/what-are-thermostatic-radiator-valves.html

Says on 1 to 5 TRV

2 c15C

3 c20C  

4 c25C 

5 c30c - essentially in most homes unrestricited on 5.

Some are actually scaled 1 to 6 - so you might need to tweak table a bit.

For many c18c - so 2.5 to 3 on B Gas scale would be enough in occupied spaces - pushing towards just over 3 - or above 21C (nhs 18-21's upper range) for those who like or need for medical reasons say in living room area - it toastier in doors.  

Although you might want to add 0.5 point to the setting if larger rooms or sitting a long way from radiators. (Even within one room - the temperature range can be a few degrees without active circulation)

Example with thermostat in hall

If your room doors from radiator het rooms with TRV control - leading onto your hall are always open - then over time the heat from them will also heat the hall - so they too will be based more loosely on the master thermostat in reality if TRV's set higher - but might be a couple of degrees off. 

But with the thermostat in an un het hall it may never trigger off - even if you heat other rooms to uncomfortably warm temperatures - e.g. if TRV set to 4 or your 5 - say behind closed doors evenings / overnight.

I know as that was how my parents used to run theirs - for a couple of years.  Until I upgraded their door contact based alarm system to PIR based.

My mum used to insist on open doors in rooms during the day. So during the day - the hall thermostat would kick in before the TRV valve - but not at night

Although they dropped the hall thermostat 3-5 degrees to as low as 12 when dad wnet to bed - when on coldest nights the boiler came back on - the living room with max TRV would often end up roasting in the morning - reducing the TRV to 3.5 solved part of that problem.

Where TRVs play a part is when can zone heat a decent chunk of property - say heat unused rooms in a larger home to say 12-15 rather than 18-21+ - when only using a couple of rooms .  Then TRVs can help cut bills by say cutting loses from unused spaces (walls, windows, roofpsace etc)  (say 12-15C for insurance or dampness / mould type minimums).

quartzz

"At that point the boiler will need to deliver less power (energy over time) as no longer heating that one space" - there might be quite a lot of technical information in that sentence which I don't know about, which means the boiler heater/motor/heating oil isn't being used un necessarily

FreeBear

quartzz said: the boiler is a warmflow KC90HEE - described by one plumber as "not the best" but that could be for any number of reasons (maybe he wanted to sell me a new one). there's some features it doesn't seem to have that I think would be useful - maybe that's why it's "not the best". I think it's a condensing combi. installed 2007

KC90HEE is a current oil fired condensing boiler first produced in 2016. Any oil boiler installed after April 1st 2007 would have to be condensing, so the exact model isn't really that important.. Being oil fired, it won't modulate, so power output will be way of on/off control of the burner. Having radiators shutting off via the TRVs will mean that the boiler should be off more than it is on. Not ideal for efficiency and long term reliability, but oil fired boilers tend to be pretty simple beasts.

Reed_Richards

quartzz said:

thermostat is in the hallway (the rads are only in rooms, with none in the hallways). 

Your boiler will be on for as long as the temperature in the hallway is lower than the set temperature on the thermostat in the hallway.  The only effect of changing the settings on the TRVs will be to do with the amount of heat that gets into the hallway.

If you make the set temperature on your hall thermostat high but set all your TRVs to a low number then water will stop flowing through all the radiators but the boiler and the pump will keep going.  Either:

1. This will strain the pump causing it to wear out rapidly.
2. A "safety valve" will operate (if fitted) causing the water to bypass the radiators and return to the boiler.  The boiler will rapidly overheat and shut down but the pump will not be strained.  

quartzz

FreeBear and Reed thanks for both. my thoughts this evening were that having the TRV's set to a low number would surely mean that some energy is being wasted (eg, the difference between "5", and what the TRV is set to).

the thermostat is in the hallway, about 6 foot away from the nearest TRV which is in the kitchen (the stuck one), with a door separating the two. I usually have the kitchen door slightly open (about one foot) to let some heat from the kitchen into the hall (the hall would otherwise get quite damn cold most of the time). but a few youtube videos have mentioned that the TRV and thermostat being close proximity to each other can "fight" each other. the thermostat is set to about 20 degrees currently, and I hear the boiler "spinning up" and water circulating around the house probably every 30-60 minutes or so (vague guess)

so far with the "eco budget" mindset I've had the 2 downstairs TRV's between 3.5 and 4 (the ones upstairs are mostly off until I am up there) , I'll try the downstairs TRV's more "maxed" at about 4.5 and see how it goes?

Reed_Richards

quartzz said:

FreeBear and Reed thanks for both. my thoughts this evening were that having the TRV's set to a low number would surely mean that some energy is being wasted (eg, the difference between "5", and what the TRV is set to).

This is wrong and I can't fathom your thought process that is making you think this.  The only way you can waste energy is by having the boiler running for longer than it needs to.

When the boiler is running you can waste energy by making rooms hotter than you need them to be.

You can also waste energy when all the rooms have reached their set temperature but the hall is still cooler than the temperature set on the thermostat there, so the boiler keeps running.