Rad always hot

[RrogerD]

This is a two-part query.
My tenant is saying that the radiator in his room is always hot. I've talked him through checking that the trv is operational. He swears it is ie it is not loose when on setting 5, the highest (thinking body has come unscrewed and so not closing off when set to zero). I suggested then to switch off the heating at the boiler. He says, still the same issue. Hence the second problem.

Query: if his rad is the first in the loop, would it still get hot even if no through-flow? Ie the trv is closing correctly but the hot water is still getting in.

The second issue, the rads heating when heating off, I guess is a faulty diverter valve.

It's a combi.

Thoughts re the rad hot issue?

 

[Wayners]

One rad shouldn't have a trv on so combi circulates to cool as it gets hot when heating water..
Normally the bathroom rad has no trv on.


Have you removed trv and checked pin moves ok? Also swap trv with another known working valve.

 

[Madrab]

If the rad has a TRV and it won't shut off then chances are the pin is seized and the TRV can't close the valve. Usually all that takes is to free up the pin. If the boiler isn't on CH mode but still heats the rad then there's something else going on. If the diverter was stuck then the rad may get hot when the HW is running but only then and it wouldn't be hot, maybe warm and it wouldn't be all the time, unless the HW is constantly running.

I would think it's time to call in your Gas bod, who normally services the boiler each year and get them to check it over.

 

[ericmark]

I came across this the other day.

Why one is able to set a TRV at 26.4ºC eludes me, or why they don't show degrees C direct, all my TRV heads are electronic and do show in degrees C.

Pre-condensing boilers, which can modulate (turn down output) we would not fit TRV heads in the room/s with the thermostat, my old house was like this, thermostat was between living and dining room, and TRV's only fitted to upstairs rooms, and no by-pass valve fitted.

But we have moved on, to the point of having linked TRV heads, no room thermostats, and the hub talking to the boiler using the likes of OpenTherm, so the boiler does not run at maximum output.

There are also many systems that run somewhere between the two will things like bathroom radiators with no TRV, but one has to look at the boiler design, and it seems some installers work on the "Well I have always done it this way, I see no reason to change." but it is not helped by the boiler manufacturers, read their installation instructions, and some have built in by-pass valve, and some need an external one.

Even with the combi boiler, some still don't modulate, and have an internal water store. Many oil boilers are like this.

I have oil, it does not modulate, and I found it could heat selected radiators even with the pump not running, therm-syphon was enough.

With all this in mind

I would think it's time to call in your Gas bod, who normally services the boiler each year and get them to check it over.

that is likely the best advice. Jumping in with comments like

One rad shouldn't have a trv on

assumes that is required with your boiler, and we simply don't know if you have things like by-pass valves.

 

[CountryFan]

What model of combi and does it have a preheat function?

 

[Madrab]

Why one is able to set a TRV at 26.4ºC eludes me, or why they don't show degrees C direct, all my TRV heads are electronic and do show in degrees C.

I think the trouble with TRV's are that they really aren't an exact science. The analogue TRV's aren't really that accurate nor responsive, whilst digital E-TRV's are considered more accurate and responsive they are still ultimately, like all other TRV's, a slave to their immediate surroundings.

For true room to room control they should all really be controlled by accurate room stats that either talk to each TRV in that room or every TRV controlled via a central control. I know that adding in these extra controls would make the implementation more expensive but without that then again then can only sense what's around them and even with detailed hysteresis, it still isn't an exact model.

 

[ericmark]

I think the trouble with TRV's are that they really aren't an exact science.

You have hit the nail on the head. I think a lot of central heating control is near enough engineering.

My Wi-Fi models at least tell me when the batteries are discharged, but I simply don't check them enough times, specially in the summer, and so each Autumn I need 20 good quality AA cells.

I have removed TRV heads to check pins, and they need a lot of effort to push them down even when A1, so trying to work out a problem over the phone, is not going to be easy.

 

[RrogerD]

Thanks all for your replies.
I'm planning (trying) to get the plumber back to have a look at it all. I suspect as suggested, it's the diverter valve and maybe the trv. For the basic cost, I'll get him to replace it anyway rather than trying to free it up. The call out charges are significantly more than the parts.
I think the bathroom towel rails are set as the 'always available' rad/s, although not sure tbh.
With regards fitting better, fancier trvs, it's not worth it tbh.
Thanks again for the thoughts and suggestions.

 

[Mister Banks]

I think the trouble with TRV's are that they really aren't an exact science. The analogue TRV's aren't really that accurate nor responsive, whilst digital E-TRV's are considered more accurate and responsive they are still ultimately, like all other TRV's, a slave to their immediate surroundings.

For true room to room control they should all really be controlled by accurate room stats that either talk to each TRV in that room or every TRV controlled via a central control. I know that adding in these extra controls would make the implementation more expensive but without that then again then can only sense what's around them and even with detailed hysteresis, it still isn't an exact model.

The Wiser system has all TRV’s talking to the hub but now there is a v2 hub available that can talk to a simple and relatively inexpensive room thermostat which works in conjunction with the TRV.

 

[Madrab]

Most E-TRV's can/will run via a central hub, all comes down to whether each room is to be considered as it's own zone then each rooms TRV's should be controlled by a wall stat in that room.

My point was that a TRV, being in such close proximity to the heat source, isn't ever going to be very accurate as far as it's setting is concerned, when considering the overall room temp.