How does a TRV actually work?

[ericmark]

OK I know basics, the head monitors air and water temperature the latter corrects the former so it shows actual room temperature and if target is higher than current it lifts the pin and if target is lower than current the pin lowers increasing or decreasing flow through valve.

However what happens in real terms? does the valve ever fully shut? or is the always a little flow? I have 4 valves with electronic heads, 3 seem to do as expected, 4th in wife's bedroom seems to have a problem, however not sure if head, base or incorrect setting, or if expecting too much.

3 valves had Honeywell bases, and one cheap base from Screwfix, cheap base in hall and that one seems to work A1, other 2 seems reasonable, only go over temperature when temperature has changed to lower value so clearly time delay, and only under temperature when again after a change or when boiler not running.

However wife's bedroom is a problem, the electronic head was fitted as she complains room too hot in the main, but some times too cold and she has piled stuff against radiator so had to assess to adjust normal TRV head, since main complaint is over temperature being able to turn radiator off remotely seemed the answer.

So this morning readings are

So with central heating off her room (Linda's bed room) does cool down, however not as much as mine (Eric's bed Room) but her room is above Living room which is set higher, so heat could raise through ceiling and floor, so latter in the day we get

where her room is much hotter than set, I have dropped hall temperature, to 19°C and her room to 12°C and swapped spacer from thick to thin in her room, to change set to 36°C and could see and hear plunger retract, on replacing set to 12°C and could hear motor run and last few seconds seemed to strain so assume is hard down, before changing spacer her radiator stayed just warm when heating running, since changing heating has hardly run, so I test bathroom radiator first with no TRV and that one has always been cold each time came to test so feeling one in bedroom pointless it will be cold as boiler not running.

So could be some thing silly like her using a trouser press, but since able to monitor her room as she had complained always seems to be too hot when heating running, so now looking at mechanical part of valve, so if radiator just warm is that a fault or normal? Could fact that her valve has been closed for a long time be a problem with poor seating, and now valve is exercised once a week at 10:30 am on a Monday will it improve.

It would be a nightmare changing valve, really hard to get to, if she was complaining of room too cold I would blame stuff around radiator, but complaint is normally room to hot.

 

[big-all]

should be on or off not trickle just heat -warm enough -off cold enough on full flow with perhaps +x-1-1.5%.

 

[ericmark]

OK so each time the eTRV head runs it should fully open or fully close valve, it is clearly not doing that, you can hear it working and it takes around 60 seconds to move full travel, but you hear it working for around 3 seconds at a time.

Set at 12°C room has warmed up from 19°C to 21°C over 3 hours this morning since the programmer has switched on central heating, and radiator is clearly warm. Valve looks like a Honeywell VT15GE with is a bi-directional wax valve, it says "Use the VA8200A001 tool for cleaning or replacement of the valve seating without draining the system." and at £17 for valve not cheap, but also not expensive.

So it seems some repairs are required, as to if cheaper to get Plumber you has the tools required to do the job, or buy a tool not sure, so now what I need is maybe ring up a plumber as price the job, but main problem is access to radiator.

 

[big-all]

they work on a wax element as far as i know so the water temperature and air temperature will effect the operation to some degree especially when a drastic change happens like pump starts and cold to hot water and may cause a short term settling down

 

[ScottishGasMan]

Electronic TRVs should be either open or shut. So apart from a period just after its closed where there is still residual heat in the radiator then it should be cold when its off.

Normal TRVs are very much the same on or off there not there to regulate flow through the radiator, they let flow in or do not, however there will be a transition period where the wax or liquid capsule is expanding or contracting where the flow has went down but not yet fully stopped.

Some electronic TRVs have a method of calibrating them to the different valve types, Im not familiar with yours but worth checking to see if thats an option. Failing that get one of the standard valve heads on and turn it right down, if the radiator still warms up then the valve body its self has failed and would need replacing to resolve the issue.

 

[ericmark]

As I read about TRV's I see so many half truths, and example is turning up the temperature on a TRV will not heat up the room any quicker, this is half true, but it depends on the built in anti hysteresis software, I have found when set to target 20°C with current at 12°C for the first 6°C up to 18°C turning the TRV to 22°C will make no effect what so ever on time to heat to 18°C however it will make a huge difference in time taken to heat from 18°C to 20°C as one has effectively bypassed the anti hysteresis software, I did exactly this, the TRV was set to 22°C at 7 am then back to 20°C at 8 am and by 8:30 am temperature was steady at 20°C, if however at 7 am I simply set it to 20°C it was 10 am before steady at 20°C.

The problem is the TRV has moved on, in the 90's my sister had banging from radiators, turned out TRV fitted to wrong side of radiator, today most TRV's don't care which direction the coolant flows, they still work without banging. But the diagrams drawn to show us how they work have not altered, clearly some thing has changed, but seems what ever has changed has been kept secret.

It takes around 7 minutes for the valve head to initialise, and around 3 minutes to motor from fully closed to fully open, in 6 minutes a fair bit of liquid will flow, the radiator would get quite hot in 6 minutes, however this time of year the radiator only gets warm, some times one has to feel it twice to be sure it has warmed up at all, so it is clear the valve is gradually opened and closed to maintain the temperature.

 

[Dan Robinson]

Electronic TRVs should be either open or shut. So apart from a period just after its closed where there is still residual heat in the radiator then it should be cold when its off.

Normal TRVs are very much the same on or off there not there to regulate flow through the radiator, they let flow in or do not, however there will be a transition period where the wax or liquid capsule is expanding or contracting where the flow has went down but not yet fully stopped.

Some electronic TRVs have a method of calibrating them to the different valve types, Im not familiar with yours but worth checking to see if thats an option. Failing that get one of the standard valve heads on and turn it right down, if the radiator still warms up then the valve body its self has failed and would need replacing to resolve the issue.

Not true dude (partly). The valve will position itself where the flow is correct for the amount of heat required. On hr92's there is a setting that tends you as a percentage where the valve is.. The last firmware update askari gives you this positioning on the main controller :

Cheap trv valves with flat seatings can be a bit of a blunt instrument as the degree of open has a much sharper curve. Better valves like the Honeywell Valencia have a conical aperture etc, so when the valve opens and closes there is a much more linear response.

 

[Dan Robinson]

 

[D_Hailsham]

they work on a wax element as far as i know so the water temperature and air temperature will effect the operation to some degree especially when a drastic change happens like pump starts and cold to hot water and may cause a short term settling down

Older/cheaper mechanical TRVs relied on a wax element. Modern/better quality versions use a fluid filled element. Electronic TRVs use a NTC thermistor, as used in modern room thermostats,to measure the temperature.

In all cases a TRV is designed to act as a proportional controller, not as an on/off one. There is a proportional band from closed to fully open, which is normally 2°C wide, within which the TRV is designed to work. If the required temperature is 20°C, the TRV should be fully open if the temperature is below 19°C, and fully closed if it is over 21°C.

 

[ericmark]

Thank you Dan, I was starting to wonder, it seems three options.
1) Drain system, swap valve, add more inhibitor and refill.
2) Get the spare parts to repair the valve including tools.
3) Wait and see if valve beds in as could be some muck under valve seat.
I do wonder if better to employ a plumber to do the job, may actually be cheaper than buying the tools?

As to number 3, not sure about valve settings, set to 15°C it is unlikely to operate the valve, maybe better set at around 20°C so valve actually moves as then more likely to dislodge any muck under the seat.

 

[ericmark]

Older/cheaper mechanical TRVs relied on a wax element. Modern/better quality versions use a fluid filled element. Electronic TRVs use a NTC thermistor, as used in modern room thermostats,to measure the temperature.

In all cases a TRV is designed to act as a proportional controller, not as an on/off one. There is a proportional band from closed to fully open, which is normally 2°C wide, within which the TRV is designed to work. If the required temperature is 20°C, the TRV should be fully open if the temperature is below 19°C, and fully closed if it is over 21°C.

Thank you for confirming that, I have now set valve to higher temperature in the hope it will actually move from time to time and maybe dislodge what every is stopping it fully turning off, it clearly does close or radiator would be really hot, but does not close fully, so radiator stays luck warm.

 

[D_Hailsham]

Have you tried swapping the head in your bedroom with that in your wife's (I assume they are both Honeywell bodies)?

Have the radiators been balanced?

 

[ericmark]

Today it seems to be living room with problem, bedroom only 1°C over temperature living room 3°C over temperature, the radiator with the Screwfix unbranded TRV seems spot on but other three radiators with Honeywell VT15 bodies seem to have a problem, I would guess Honeywell VT15 are around 12 years old and the Screwfix is 1 year old, I am wondering if I need to change all the TRV's? or at least have the valve seats changed?

 

[Dan Robinson]

It's the heads that control things. Not the bodies.

 

[D_Hailsham]

I just wonder if these new e-TRVs, with their two temperature sensors, are as good as the manufacturers claim.