Combi Boiler Loosing Pressure


Postby drpaul » Wed Oct 01, 2008 7:30 pm

I have a Baxi Combi instant 80he that looses pressure overnight. I have changed the pressure relief valve but it's made no difference. Is there anything else I could look at? All my pipes go through the loft and no leaks apparent and cant really afford a plumber to come out. Any help on what else could cause this would be great.

Thanks
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Postby chris_on_tour2002 » Thu Oct 02, 2008 7:30 am

eliminating the obvious, have you bled the radiators? could air be getting into the system?
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Postby htg engineer » Thu Oct 02, 2008 7:51 am

When using the heating or hot tap, does the pressure rise ?

could be the expansion vessel at fault


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Postby drpaul » Thu Oct 02, 2008 4:48 pm

Thanks for the replies.

I have bled the rads and everything seems fine, and yes when the heating is on the pressure rises sharply to just over three bar.

Am completley stumped :?

Any help would be great
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Postby screech » Thu Oct 02, 2008 11:50 pm

there's no air in the expansion vessel. it's behind the boiler. these boilers are not that well designed, the expansion vessel is too small and if you have 8 radiators or more (less than 8 if they're large) then you need an additional one.

to repressurise you need to open a drain point on the boiler when using a foot pump to pump it up to make sure you only pressurise the vessel not the whole system. access is over the top of the boiler.
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Postby Steve the gas » Fri Oct 03, 2008 4:41 am

As Htg says pressure vessel at fault- replace
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Postby screech » Sat Oct 04, 2008 11:44 pm

replacing the expansion vessel on these boilers requires removing the boiler from the wall
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Postby htg engineer » Sun Oct 05, 2008 6:43 pm

Fit an external pressure vessel - you don't have to replace the one fitted to the back of the boiler.

External = DIY job
Replace existing = CORGI engineer required


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Postby screech » Tue Oct 07, 2008 9:07 pm

the trouble with these boilers is the standard ex[ansion vessel has a store of hot water in it. you can fit an external one but if the standard one is packing up it's more than likely that the system required an additional vessel in the first place. standard ones only have a capacity of about 6 litres after you take away the space the store of the h/w takes up. go for a vessel 10 litres or more. 8 is the absolute minimum i'd fit.

it's lucky if the diaphragm separating the system water and air has gone. if it's the water store one that's split then it's definately a boiler off the wall job to replace the standard vessel, then add another vessel to stop if happening again. sounds like the water diaphragm is still fine though as that would constantly overpressurise and never drop.
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Postby drpaul » Fri Oct 24, 2008 8:14 am

Hi,

I've got the original heating installer coming around tomorrow. He is going to fit an external tank which sounds ok. One plumber quoted £500 for two of them to do the job in 4 hours including removing the boiler from the wall. It worked out at about £50 an hour each !!! Not a chance.

The other plumber is fitting the external tank for fifty quid and I got the tank and inhibiter and connector for forty.

I hope this is the right way about this. Money wise it's alot cheaper, I just hope its ok in the long run as i'm not planning on moving.

Many thanks for everyones advice

Regards

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Postby htg engineer » Fri Oct 24, 2008 9:35 am

The price you're paying is about right.

was the £500 for an external pressure vessel ?????

How many hours ???? even removing the boiler and fitting the integral vessel wouldn't take 4 hours. I think you found the rip-off merchants of your area.

This should solve your problems. Integral and external vessels do the same job, it's not a problem fitting an external one.


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Postby drpaul » Thu Oct 30, 2008 8:30 pm

Hi,

We had an external tank fitted today, all drained, bled, new inhibitor put in. However the pressure is still dropping the same as before but not as quick.

Any other ideas?

Getting frustrated now

Regards
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