Worcester Bosch 37CDi losing pressure - but why?

[fathertobe]

Our combi boiler keeps losing pressure. But not in a standard way.

I happened to check gauge recently on one day and it was fine. Then the next day I noticed it had lost all pressure. Suspected a leak. Checked ceilings etc, but nothing. Can't check under ground floor rads easily.

Repressurised boiler (took about 20 secs) and called WB. Engineer visited few days later and he repressurised expansion vessel (though I wasn't convinced he was sure that was the problem).

All fine for a few days until this morning - I noticed the pressure had dropped about 1/3 bar. Didn't do anything but returned just now to see needle on zero.

So far I've:
1) Checked for obvious leaks - ie stains on ceilings. Nothing.
2) Checked overflow pipe outside. Nothing.

Any ideas? Really grateful for help.

EDIT: My problem sounds a lot like this one: //www.diynot.com/forums/viewtopic.php?p=491337#491337 in that the pressure is also getting higher than normal when the heating is on.

 

[twgas]

If the vessel was repressurised properly I would suspect the connecting pipe between vessel and boiler is blocked.

 

[fathertobe]

Thanks for this. Guess I'm calling them out again.

 

[fathertobe]

Well, 2nd callout resulted in nothing more.

PRV replaced - more out of desperation than anything else.

Basically:
1) Pressure is (when cold) about 1 bar
2) When heating is on, pressure can creep as high as 2.5 bar.
3) Generally the pressure sits at 1 bar but occasionally it drops below the 1 bar mark - dropping to about 0.5

I'm stumped.

Would really appreciate help.

 

[petertheplumber12]

how many rads have you got? if there are too many you may need an extra expansion vessel.

 

[fathertobe]

Hi peter,

Thanks a lot for replying. Yes, a few people I've spoken to have mentioned this. I've got something like 14 rads - and they're quite large (column things).

What perplexes me, however, is why this has only just started happening?

If this is the way forward, however, any idea of a guide price to fit this? Appreciate you may not want to answer that. I'm in London, btw.

Thanks again for answering.

 

[petertheplumber12]

it is definitely something you need to do 14 rads is too many, volume is to great, if you want it done really cheap, choose a rad not too small, that you don't mind loosing 75% of the heat and drain 3/4 of the water out of it, and DON'T bleed it. it will work as an extra expansion vessel. Or get one fitted, I did one to a boiler in Essex a few years ago and charged £150 labour and material. It may be a bit more but it only takes a couple of hours to fit so no prob.

 

[fathertobe]

Thanks a lot Peter. Really appreciate this help.

Will post back what I eventually do so someone can read this in the future.

ps assume your work never takes you near hackney...? (Not even sure whether I'm allowed to ask this...)

 

[petertheplumber12]

you are allowed to ask, I live outside the m25 in surrey so no not really.

 

[fathertobe]

ok. Thanks for answering.