Anyone care to diagnose my central heating problem?

[MaudantWit]

As it has suddenly got so much colder, we have put the CH controls onto "on all the time". The thermostat is set to 20+, and the TRVs are set to 5, and yet the temperature in the sitting room is 10 degrees and the radiator is stubbornly refusing to come on.

Are we making an elementary mistake or is some part of the system kaput?

Where abouts in the house is the thermostat?

The thermostat is in the hall, which also feels very cold. I dimly recall from other threads that the thermostat shouldn't be in the same room as a radiator with a TRV, but that isn't the case here.

Change the batteries in the thermostat?

Do all the other radiators come on?

Have you tried bleeding it?

Are both valves of the radiator open?

We've just had this. Flow valve had gone.

if your boiler is working (eg you have hot water) and thermostat appears to be calling for heat (and is not eg out of range if wireless, or out of battery, ie is definitely communicating with boiler) then flow valve is most likely. 15 min job for a plumber to replace.

turn off every other radiator in the house. Does it, or either of its pipes, now heat up?

When did it last work?

What do the knobs on the radiator valves look like? (photo preferred)

Thank you for your replies. I have retreated to bed, to keep warm, so can only answer some of your questions:

Boiler is working - we have hot water - but we are already waiting for our plumber to call because the system never really switches off (I forget the exact diagnosis, but a valve in the airing cupboard is stuck in the wrong position, meaning that even when the system is off, it is on).

Upstairs radiators all seem to be on, but after posting I noticed that the dining room radiator was cold, too.

Do thermostats have batteries in? As you can tell, I am a domestic numpty, but will investigate that tomorrow.

Oh, and I suspected that the radiator wasn't working on Thursday evening, as it was stone cold (but maybe it had turned itself off as we had the log burner going, although the room did not feel particularly hot), but it was tepid on Friday morning.

Are the two problem radiators completely cold? If not and the bottom is warm then bleed. If to only is warm then could be sludge in radiator. If cold could be a blockage or air pocket or balancing

We had this problem last year - the upstairs radiators were toasty warm but the downstairs ones were freezing cold. However, if we switched the hot water off but kept the heating on, the downstairs radiators would warm up (a bit).

Gas engineer (BG service contract) said that the valve that switches between hot water and central heating was probably full of sludge and recommended a power flush. It didn't help that the pipe that fed the downstairs rads was narrower than the one that fed the hot water cylinder (or at least narrower than it should have been).

Yes, the two downstairs radiators are stone cold. I am wondering whether this is linked to the problem of the hot water never being off because of the stuck valve in the airing cupboard.

turn off every other radiator in the house. Does it, or either of its pipes, now heat up?

When did it last work?

What do the knobs on the radiator valves look like? (photo preferred)

As I said, it last worked on Friday when it reached the heights of tepid.

I will do the turning off of all other radiators tomorrow morning.