Combi Boiler Pressure Build Up and Loud Banging

[mozzo]

I would be very gratefull if someone can give me a clue as to what is wrong with my combi.

It's a Ravenheat approx 8 yrs old. It's been a good boiler but recently, when the boiler switches on from very cold i.e. 1st thing in the morning, the pressure on the gauge rises from 1.0bar to 3.0 bar, there is loud banging and after a minute, steam starts to vent from the top of the boiler. Obviously, I switch it off immediately, I leave it to settle, the pressure slowly drops back to 1.0 bar, I switch on again and it runs perfectly.

Can anybody help?

 

[kevplumb]

try a search on expansiom vessel

 

[mozzo]

Thanks for the response Kev.

Can you confirm that the expansion vessel can be recharged using an ordinary car foot pump?

 

[kevplumb]

yup drain the boiler first tho

 

[mozzo]

Sorry if I sound like a total idiot.

How do I drain the boiler?

 

[kevplumb]

close the valves on the two big pipes and open the drain on the boiler
or loosen a joint
when you need to repressureise it post

 

[ChrisR]

I don't see the connection between the pressure vessel and the behaviour. Perhaps I'm having a senior moment? No single obvious cause I can see, but the pump could be sticking.

If your pressure shoots up then yes you do need to recharge the pressure vessel - as described here many times - we need a FAQ section!

 

[kevplumb]

totally agree mate

the sparks have one (very informative )

 

[mozzo]

Thanks for all your help guys.

Will try it out tomorrow.

 

[mozzo]

Thanks again for all replies.

When one problem clears, another one appears.

I drained the boiler, pumped up the expansion vessel to 0.8bar, closed the drain valve, filled the system to 1.4bar and switched on.

The heating worked fine, pressure rose to 1.7bar when the system was up to temperature so that seemed fine.

The problem is, now the hot water doesn't work!

When the tap is turned on, the boiler fires, hot water comes out of the tap and then runs cold. I don't understand ow this can happen. Where is the heat from the burner going if it is not heating the water?

Any help would be greatly appreciated!

 

[mozzo]

Could it be the thermostat?

 

[kevplumb]

run the hot water and feel the ch flow pipe

 

[Slogger]

8 yrs old me thinks it is trying to tell u summit like replace me please get one of them new condecending combi boilers ( or is it condencing) 8 yrs now what king of car would that be if it was a car >? a banged up escort or worse

 

[croydoncorgi]

For the pressure to 'shoot up' even with the vessel only partly charged, there must be something else wrong.

Also, if the vessel pre-charge has been lost, chances are its diaphragm has a hole in it. So recharging will only have a temporary effect, until the air disperses. The only situations where recharging the vessel will ever have a lasting effect is when it's been accidentally discharged - usually by someone mucking about with the Schrader valve when they should have left it alone - or when the standard pre-charge is not enough to cope with an unusually high static head.

OK - the diaphragms in old vessels can sometimes let air diffuse through slowly but it's only the top of the Slippery Slope down to the scrapyard!

 

[mozzo]

8 yrs old doesn't sound old for a combi boiler.

I've seen houses with 15-20 yr old boilers working perfectly. Besides which, being quite a green kind of guy (not to mention carefull, moneywise), it's not really on all that much so I wouldn't expect to have to replace the boiler.

Anyway, that's besides the point. I left the H/W water running for about 15 mins and it was still running lukewarm so I left it.

Went back 1/2 hour later, ran the hot tap and hey presto - hot water.

Don't know what's changed in that 1/2 hour but it works now.

Any ideas? Is it likely to re-occur?