Re: Cold Radiators

I should have mentioned one of the rads has a thermo-valve; the other one just plain on/off valves.

The recommended way is to remove the head and ‘tap’ the body of the valve firmly. Pulling the pin is not recommended. Generally, a couple of firm taps and the pin will move. A ‘twist’ of the pin is ok. Pulling is the problem.

If you don’t have a thermostatic valve, one valve should have a knob on it, the other just a cover.

Open the one with the knob on fully.

Then, use the knob to close the other one, counting the turns to close it. ( Probably not many.) Then fully open it. Check the rad gets warm with the heating on.

If it does, close the second one back to the original position. It isn’t unusual for the second valve to only be open under one turn in some locations.

you probably have an airlock somewhere. A flat out circulation pump may get it to a radiator.

Otherwise if pipes are routed through the roof check for temperature there.

Have the radiators ever got hot?

How long have you noticed that they are no longer getting hot

Have you had any work done where the system has been drained?

Have you had new radiators installed elsewhere in the house?

There are a few common reasons why radiators do not get hot and it helps to know if anything has changed on the central heating system.

It's sorted. Turns out the two rads had been plumbed in in series with one another even though they were in different rooms. So if one's valve wasn't working and closed shut, both rads would be cold. And that's what happened here. The rad causing the problem had a thermo valve which had got stuck. Removing the thermo head and joggling the pin underneath freed it up. Once that happened, both the rads got hot. Thanks to all who chipped in with ideas here, but that suggestion was the money shot.

Glad you've got it sorted but the installation that you have described is totally unsatifactory, and the problem - or something similar - will continue to occur. With 2 rads in series, if the TRV turns off or reduces the flow, this will affect the radiator in the other room regardless of its room temperature. You really need to sort out the pipework so that the rads are in parallel. In the short term, simply leaving the head off the TRV will help.

In the flat I had years ago the radiators were all plumbed in series, with a single pipe going around the flat in a loop. The secret was that the in and out pipes both went into a single valve at one end of the rad and the valves instead of being on/off were through/bypass, so if the rad was "off" you got a short circuit, rather than the more usual open circuit.

Never took one apart, but I assume the valve had a long tube inside the bottom of the radiator to deliver hot water to the other end so that there was flow through all of the radiator.

It confused people no end!

Anyway, maybe you could use valves like that on your series branch!

nib

On some microbore systems there was a "long tube inside the rad" because it was all fed from one end.

I am fairly sure that the rads were not all in series though - there was some sort of manifold involved ?

(Mine were not microbore, and def a loop, I traced the pipework! nib)

Fair enough - but I have to say that I suspect the long tube variation is very unusual on a system that isnt microbore

Not that unusual you still see it in commercial situations where one pipe wends its way through a series of rooms with radiator’s flow and returns just tapped off the single pipe. First ever central heating system my parents had installed was like that way back in the 60’s.

As a quick and dirty solution for the OPs two radiators it might be an idea to pipe between the flow and returns and that means the individual TRVs only affect their own radiator.

Richard

That might work, but it's more likely that the water would take the line of least resistance and flow through the bi-passes just created rather than through the valves and radiators.

The single pipe systems in commercial buildings invariable have one side of each radiator connected at the top and the other side at the bottom, so that there is a thermo-syphon effect.

Worked alright on my parents system

It was the norm in older systems, although the pipes tended to be much larger in diameter.

I recall the Grammar school I attended, which I believe was built in the mid 1930s, had large diameter pipes like scaffold poles and heavy cast iron radiators. Certainly some of the radiators were in series. Possibly not the whole school but groups of classrooms, there were issues with pupils turning one off and the classes being freezing.

Possible not too much of a problem where all the radiators are in one room but in a domestic property it's more common to have one radiator per room.

I once worked in a converted warehouse building where the conversion had been to install a lot of internal walls to separate various departments. Unfortunately no-one had considered where the room thermostats were situated so the heating for one area was controlled by the thermostat in a completely separate area. This was also where they decided that "managers" had to have offices and these were all situated on the walls with the only opening windows to the outside. The building got rather hot in summer, except for the small offices. Often too cold in winter and usually too hot in summer - what more do you want to get a efficient working environment?

Even in modern schools getting the temperature right is difficult.

I taught (as a second career) in a virtually new, specialist block which was only a year or two old. The school had been awarded specialist Mathematics Status and the Maths Block was built as part of that. The rest of the school wasn’t that old - late 1960s and 70s.

In our block, while we had individual thermostats and, I assume the rads were controlled by zone valves, the thermostats had ‘cages’ over them.

I soon discovered the my room was far too warm. Especially as we had strict uniform rules. No top buttons undone, jackets must be worn, …. I confess, I relaxed the rules during lessons. Even so, in the end, I removed the cage and turned down the thermostat.

When asked, I explained I made the pupils work harder to keep warm. 😂

At the end of each lesson, provided ties and buttons were done up, blazers on, was all checked, all was well.