What have I done to my central heating?

[Haple55]

A few weekends ago 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. I've been round and checked all the radiators - I can't find any leaks.

After speaking to friends,I was told I might have screwed it up by doing the bleeding while the system was on. I went and redid it while everything was off and cold...and it does seem to have got a bit better...but it's still not right, and needs topping up every couple of days. And I'm still a bit spooked by the way the pressure varies so much from time to time - I expect it to go up when the heating's on...but it seems to fluctuate by 2 bars, from too low for the heating to fire up to right at the upper limit - with no new water let in.

Any suggestions much appreciated.

 

[Gasman28]

It sounds like the expansion vessel requires re-charging - see FAQ's for details

 

[MANDATE]

If your getting a 2 bar rise, It may well have gone high enough to open the Pressure Relief Valve, which causes it to drop again.
Sometime the PRV does not seal properly which allows the pressure to drop.
This most likely stems from the expansion vessel having lost some of its air charge. When this happens water takes up space in the vessel which should be occupied by 'air'. The volume of air is reduced and when compressed produces a rapid rise in pressure.
The air that you bled from the radiators would have been acting like a expansion vessel, which has solved one problem but highlighted another.
There seems to have been quite a few expansion vessel problems recently. If you read about them you may get a better understanding of what's happening

 

[Haple55]

Thanks for getting back so quickly. I've been poking around in FAQs trying to find info on expansion vessels (without much luck, it has to be said!) I'll have another look tomorrow, and look at pressure relief valves too. Sounds plausible though. Could I have caused this whole problem by bleeding the system while it was on, then letting in too much new water? And if it is expansion vessel and/or PRV, is this the kind of thing I might be able to sort out, or should I get someone in? (I can do basic stuff - I maintain a bike, put up shelves and fit taps...but I've never done anything much with central heating, beyond bleeding radiators (badly)) Thanks again.

 

[heatingeng]

It sounds like the expansion vessel requires re-charging - see FAQ's for details

i would agree

 

[TicklyT]

Air trapped in radiators can mask the effects of a failed expansion vessel. Bleeding the radiators hasn't caused the problem, it has highlighted a latent fault in the expansion vessel.

 

[Agile]

What make and model of boiler is it?

I seem to have had a run of failed EXVs lately.

Tony

 

[Gas2Air]

I'm visiting lots of "my pressure is high, will it explode?". Lots of posts on here too.

The end of the world is nigh i tell you.

 

[Haple55]

It's a Worcestor Bosch - not sure of the model...I'll find out. One of their smaller ones though, I think. 28i comes to mind, but that might be wrong.

 

[Haple55]

Yup - Worcestor Bosch 28i Junior...about five years old.

 

[nogoodatfaultfinding]

Yup - Worcestor Bosch 28i Junior...about five years old.

Can i ask when you last had it serviced?

 

[Haple55]

You can. Dare I admit, never?