What's up with my central heating?

[Over The Hill]

I do not know about the combi types with pressure expansion bits, but if you have a header tank....

If you have air in the rads then it is getting there from within the water carried as bubbles which are settling. As the system is under pressure any hole will let water out not air in.
Pressure (from water expansion) is accomodated by way of a tank in the loft that is half full when cold but fills up more as the water expands. This tank also has a pipe hanging over it that air vents out of the system through.
If your pump is set too high it can push water up and out through this pipe (you may not know as it simply drops back into the loop via the header tank).
With heating on (and house hot) check the header tank to see if water is running into the tank from above. In doing this it takes air into the water. To sort it out you should be able to turn down the speed of the water pump (most have three speeds).



Somtimes it may just be down to the systems design, that pulls air out of the water without venting it off. Above is a self bleed valve that should keep the problem sorted out. To fit it you do not need to drain the system - just shut off the radiator taps on both sides to isolate it (do when it has lots of air in it) and swap over the valves.

 

[highpeak will]

Its worth checking that your filling loop is completely shut off. It could be still letting some water through, even a small amount will soon build the pressure up to 3 bar and then it will start to come out of your pressure relief pipe outside. The pressure gauge will fluctuate depending on wether the heating is on or off. It will go up about half a bar when the heating is on. Thats completely normal and would have been doing that before.
As said before bleed all your radiators when the heating is off and everything is cold, starting from the lowest radiator in the house and finishing with the highest. When they are all bled top your boiler up to 1 bar and then disconnect the filling loop to make sure it can't let anymore water through. When the heating is on it will go up to around 1.5 bar.
If it still goes up to 3 bar it is most likely a problem with your expansion vessel which might need repressurising or changing. If the pressure drops it is a leak on the system somewhere, possibly from the pressure relief valve as this is a new problem since you topped up your system.
I hope this helps. To be honest it could be many things but these would be the first things that I'd look for.
Good luck

 

[swee'pea99]

Thanks very much for all responses. It's a combi boiler and I don't think there's a pressure loop (there's certainly no tank), but tomorrow I will shut the heating off, let everything go cold, then bleed again, starting from the ground floor & working up. Wish me luck!

 

[andytheflyer]

Hi SP,

I had the same problem with a combi boiler installed in 91 (new house). We always seemed to get air in the rads over the last 5-6 years - forever bleeding them and topping up the system.

Until one day last summer, in bare feet, I stepped on a wet patch of carpet in our lounge, next to the radiator. Closer inspection showed that the TRV was dripping - and we'd never noticed. I'm certain that carpet had never been wet before -or maybe not wet enough to notice.

Had them all changed and now we never have any air, or any pressure drop on the boiler pressure gauge (a new - 2008 - Worcester Combi). What amazes me is that despite looking, I never saw any leaks and yet the pressure dropped over a matter of only days before the TRVs were changed.

So, if you have TRVs, check them very closely - that may be the problem.

 

[slowmotion]

It looks like everybody has been talking at cross-purposes. If swee'pea99 has a combi, he has a sealed system for his central heating. If you bleed the radiators on a sealed system, you have to replace the air bled out with water. This has to come from somewhere... usually a filling loop through a valve temporarily connected to mains pressure cold water. As the system is filled again with water, the gas in the pressure vessel is compressedso that the whole shebang is under pressure (typically 1 bar) when the system is working. It isn't that complicated, but you do need to know a little about it. There is loads of stuff on Google if you feel up to it. Otherwise, call in those thieves known as "professional" plumbers, and offer up a few Hail Marys

Sorry, I have not been that much help.

 

[ASC1951]

It looks like everybody has been talking at cross-purposes.

I don't think so.

If swee'pea99 has a combi, he has a sealed system for his central heating. If you bleed the radiators on a sealed system, you have to replace the air bled out with water. This has to come from somewhere... usually a filling loop through a valve temporarily connected to mains pressure cold water..

That's exactly the same system as I have, which was why I suggested this; as have others.

Anyway, swee'pea, how did it go?

 

[swee'pea99]

Sorry not to've noticed your polite query Asc - I went away for a bit to see if it would 'settle down'. It has...a bit. Having said which, I've followed the advice earlier in this thread and posted this on DIYnot.com:

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.

Now to see what if anything turns up!

 

[slowmotion]

Post the boiler badge plate. It will tell us all more.

Maximum respect to all posters here above.