Radiators not hot - but were yesterday

[smifferific]

Hi all

Glad to have found my way here following closure of the Fool boards.

Our heating has been working fine so far this winter, until this morning when it's finally got proper cold!

Boiler comes on, radiators are warm but not hot. They were hot last night though.
Boiler seems to switch on and off very frequently.
We had similar problems last year and plumber fitted a new pump.
Pump is definitely running and not making any funny noises.
I have bled the radiators.?

What next?

Thanks in advance

smifferific

[88V8]

As I said in another thread, radiators should never need bleeding.

Anyway... if the boiler is cycling, that may mean it can't get rid of the heat. Is there a motorised valve controlling the flow to the heating?
Check it's fully open.

Or the boiler thermostat is faulty or has been turned down.

Or if the boiler has an exhaust fan, it may not be running. Listen to the exhaust outside.

V8

[simoan]

I am not a heating engineer, but we had a problem like this recently and it was the thermostat. In our case the heating eventually stopped working completely because both the room thermostat and the boiler thermostat failed. However, I would imagine your problem may be due to one or the other.

Only trying to help!

All the best, Si

[Slarti]

As I said in another thread, radiators should never need bleeding.

I've never known a system where they didn't at some point, domestic or office.

Slarti

[pompeygazza]

When you bled the rads did you top up the system afterwards?

[88V8]

Bleeding.... well, in the system I installed in our previous house, they never did. Installed 1982, left there 2012. Ditto the previous one but that was only 1977-80
Mind you, the time I spent designing and installing, if I'd been a plumber I'd have gone bust many times over.

Why do rads need bleeding? I bet the number one cause is insufficient water treatment chemical. That causes corrosion, and the gases can be smelt as 'rotten eggs'.
And then, there's bad design. Wrong position of pump relative to the vent, leading to pumping over and aeration. Sometimes exacerbated by excessive back-pressure due to small-diameter pipe.
Aeration due to leaks and new makeup water.
Kettling in the boiler.
Pipe runs with air pockets.

It's all avoidable, one way and another.

V8

[smifferific]

Thanks for posts and suggestions - much appreciated.

Motorised valves are working and open
Listened outside to exhaust fan and it was making suitable noises
Although I "bled the radiators" there was only one with any air in and that only about 2 cu inches worth
Boiler temp dial near max (about 8/10) so definitely hadn't been turned down

I did actually end up turning down the boiler thermostat to see what would happen - ironically rads are now somewhat hotter! Perhaps an unhelpful interaction between sensors in different parts of the system?

Let's see what happens next (and more importantly tomorrow morning)

Cheers

smifferific

[simoan]

Thanks for posts and suggestions - much appreciated.
I did actually end up turning down the boiler thermostat to see what would happen - ironically rads are now somewhat hotter! Perhaps an unhelpful interaction between sensors in different parts of the system?

This is what happened on ours but the heating didn't work at all until you turned the boiler thermostat down! It needed to be replaced because it was not switching properly. In the days before, I noticed like you that the radiators were not getting as hot as they should, so the symptoms were exactly the same.

All the best, Si

[Slarti]

Bleeding.... well, in the system I installed in our previous house, they never did. Installed 1982, left there 2012. Ditto the previous one but that was only 1977-80
Mind you, the time I spent designing and installing, if I'd been a plumber I'd have gone bust many times over.

Why do rads need bleeding? I bet the number one cause is insufficient water treatment chemical. That causes corrosion, and the gases can be smelt as 'rotten eggs'.
And then, there's bad design. Wrong position of pump relative to the vent, leading to pumping over and aeration. Sometimes exacerbated by excessive back-pressure due to small-diameter pipe.
Aeration due to leaks and new makeup water.
Kettling in the boiler.
Pipe runs with air pockets.

It's all avoidable, one way and another.

V8

Only if you are the one designing and installing the system. All systems I have experience with, going back to about 1964, were designed and installed by other people and often not my responsibility. But at one time or another I either bled them, or had the maintenance guys do it for my comfort.

Slarti

[twotwo22]

Might I suggest that, yes, the pump is running, but only slowly, due to build up of crud ?
You could wait until the system is off and rotate the pump impeller with a screwdriver down the centre hole to make sure it turns freely.