Britony combi 80 0 pressure reading

[fluxo]

Hi,
I'm trying to work out what's going on with my chaff britony combi 80 and any help to understand the problem would be most appreciated.

The pressure gauge shows a reading of 0 - 0.2 bar when cold. But the system still runs OK for CH and DHW. I've topped it up to 1.5 bar when it's cold but when it next starts CH the pressure reading goes up to 3 bar and it vents water from the overflow / pressure relief (metal pipe outside). I've had a look around and I can't see any leaky pipes / rads / valves - there are no damp patches on ceilings under the rads.

I've seen a similar post to this but in that case the system wouldn't come on at all once it reached 0 bar - it was the flexi pipe full of sludge.

Any ideas?

I'm thinking that either
(a) there's a leak I can't find
(b) the pressure gauge is lying / broken
(c) the flexible pipe to expansion vessel is blocked
(c) or it's something else!

I just want to make sure that there's nothing I'm missing and maybe to have a good idea what to ask the plumber if / when they come out.

Cheers
toby

 

[Agile]

You dont say if you have checked the expansion vessel.

Its explained in the FAQ section on this site and if its not OK then you already know about the blocked communication pipe. ( Unlikely on that model )

Tony Glazier

 

[fluxo]

Hi Tony,
just checked expansion vessel and it was about 0.5 bar so I've topped it up to 1 bar with my trusty footpump. I've also topped up the water to 1 bar (it was reading pretty much 0). I'll let the CH run for a bit to see what happens...

cheers
toby

 

[Agile]

The ex vessel should have been topped up to 0.8 Bar but it is ESSENTIAL that is done with the system open to the atmosphere !!!!!!!!!!!!!!

Tony Glazier

 

[fluxo]

OK. I've found the longer "how to pressurise the system" faq - I'd seen the short version.
From that I take it the pressure reading I got was probably meaningless as the system wasn't open to the air. I've dropped it back down a bit (only took about 4 pumps to raise it up).
However even in the 5 mins the CH was on the pressure gauge on the system went from 1 to 2 so could I be correct in pointing the finger at a blocked hose to the PV?

 

[fluxo]

I meant blocked hose to expansion vessel.

 

[Agile]

The test for a blocked communication pipe is to leave the pump on the vessel and repressurise the water to 1.5 Bar and see if the pressure on the pump gauge goes up to about 1.5 Bar as well. If so no blockage!

Tony

 

[fluxo]

I'll check that out.
thanks Tony

 

[fluxo]

Evertything has cooled down, the pressure gauge on the front again reads 0 and I can see evidence of water from the pressure relief pipe outside
Expansion vessel pressure = 0.8bar
Added water to bring front pressure gauge reading up to 1.5bar
Expansion vessel pressure = 0.8bar

Conclusion: blocked pipe to expansion vessel.

Any idea how long it would take a plumber to repair such a fault so I can get some quotes? I appreciate that "it depends..." (I'm a service engineer too, though on different things) but a guideline is good to have.

cheers

 

[Gasguru]

Depends on access to exp vessel pipe.

Some boilers would necessitate exp vessel removal to remove pipe and clean.

If the blockage is on a bend it may be impossible to clean. It is often easier (and cheaper) to leave the existing vessel in place and plumb in a new expansion vessel external to the boiler (eg perhaps in a cupboard underneath).

Remember to release the pressure in the vessel before you dis-connect the pipe, otherwise you will get very wet if the blockage suddenly clears

Since the vessel pipework is blocked it is likely the system is in a poor state - this is indicative of a botched installation and lack of inhibitor.