What's up with my central heating?

[swee'pea99]

Sorry, didn't know where to ask, but I seem to recall somebody out there knows about this sort of thing - the cafe seemed the best place to put it.

Last weekend I bled the radiators. Hadn't done it for a long time, and there was quite a lot of air in a couple of them. So I wasn't surprised when I had to let more water into the system to bring the pressure back up. But since then, the pressure's all over the place. Mostly it's too low - I've had to dribble water in throughout the week. But sometimes it shoots up to near or around the maximum. It seems to fluctuate depending on whether the central heating's actually on too, which I'm pretty sure it didn't do before.

I've been round and checked all the radiators - I can't find any leaks. It's got me completely baffled. Anyone have any ideas? I'd appreciate it.

 

[Crackle]

Is it the pressure release valve in your boiler. Pressure builds and then it vents and you need to refill it. Check outside to see if there's water dripping from the vent pipe. Or, maybe you've a faulty expansion tank.

 

[ASC1951]

I had a similar problem with my system and it turned out that I had caused it by bleeding the radiators with the heating on, so that I was getting air back into it at several points which then made its way slowly back to the pressure vessel. Some systems can be bled with the pump running, but not mine.

Once I re-bled it all systematically with the heating off, it was fine.

Worth a try.

 

[Brains]

If the system has been around for a few years it's worth having it cleaned, we must have got out 2 bucket loads of gloopy gunk from out from out 11 raditator system that was installed in 1993.

The pump does not appreciate it, and more to the point nor do modern boilers, as they pass the water through multiple very small tubes to heat it up

 

[swee'pea99]

Thanks both - but particularly ASC1951 on account of that definitely has a ring about it - because the heating was on when I was doing it, now I think of it. As you say, certainly worth a try. (I'll check the vent pipe too, but I have a good feeling about ASC's suggestion.)

 

[trustysteed]

silly question but how do you bleed it with the heating off? what pushes the air out if there's no pressure running?

i have a similar problem with the small radiator in our downstairs loo. i have to keep bleeding it every couple of weeks, it's the only one that does it. (always done it with the heating on)

 

[threebikesmcginty]

I'd go along with ASC1951's suggeston too - the pressure varies with water temp.

Bleedin' radiators!

 

[Globalti]

silly question but how do you bleed it with the heating off? what pushes the air out if there's no pressure running?

i have a similar problem with the small radiator in our downstairs loo. i have to keep bleeding it every couple of weeks, it's the only one that does it. (always done it with the heating on)

If your system is conventional with a header tank then the water pressure forces the air out of the bleed valve.

With a combi boiler I'm not sure.

If you are continually bleeding your system you could be accumulating hydrogen gas, which is coming from internal corrosion. Try holding a match nearby next time you bleed. If it's hydrogen you need to top up the Fernox in the system, it contains a corrosion inhibiter.

 

[trustysteed]

If your system is conventional with a header tank then the water pressure forces the air out of the bleed valve.

With a combi boiler I'm not sure.

If you are continually bleeding your system you could be accumulating hydrogen gas, which is coming from internal corrosion. Try holding a match nearby next time you bleed. If it's hydrogen you need to top up the Fernox in the system, it contains a corrosion inhibiter.

it is a header tank so will try that thanks.

hold a match to a hydrogen leak? are you mad, man? ive seen the hindenburg film!

 

[ASC1951]

silly question but how do you bleed it with the heating off? what pushes the air out if there's no pressure running?

Gravity. Do the downstairs ones first. You may have to refill the pressure chamber before you do the rest.

 

[threebikesmcginty]

Gravity.

What's that?

 

[fossyant]

We only ever bleed one radiator - seems to be where the air ends up..odd. Only do it every 6 months but as said, system off.

 

[slowmotion]

If you have a Feed and Expansion (header) tank, you won't have a pressure vessel, surely??

 

[bad boy]

I know this might sounds silly but have you done the bleed nipples up properly loosing pressure is a sign of a leak normally.

Check also around the bottom of the rads where the trv valves are they can sometimes leak there.

 

[Globalti]

You need to go and ask on DIYnot.com, there are real plumbers on there!