combi boiler problem

[kpp]

hi all,
i have a combi boiler, gauge reads just above zero, when heating comes on pressure rises to 3 bar and relief valve operates, expansion vessel schroder purges air when depressed, all rads are hot and have bled, no safety has operated apart from relief valve. gauge appears to operate ok eg rises when pressurised, operates at 3 bar. any ideas?
regards kev

 

[Mbear]

hi all,
i have a combi boiler, gauge reads just above zero, when heating comes on pressure rises to 3 bar and relief valve operates, expansion vessel schroder purges air when depressed, all rads are hot and have bled, no safety has operated apart from relief valve. gauge appears to operate ok eg rises when pressurised, operates at 3 bar. any ideas?
regards kev

does the boiler have a flexihose from the manifold to the expansion vessel? If so these flexihoses can choke with sludge/magnatite causes the same symptoms as a flat expansion vessel. Example vokera compact. Alternatively if the boiler is a baxi 105preheat, it could be the fact that there are to many large rads on the system and the exp vess can not handle the expansion. Fix for this issue would be add an external vessel to compliment the internal vessel

 

[oldplumber]

expansion vessel may have lost its full charge, isolate central heating cicuit at boiler feed and return, drain off excess pressure via prv and check pressure in expn vssl and recharge to manufacturers req pressure. open up heating circuit and recharge to working pressure (1 bar) and check that heating works ok and prv doesnt blow off again.

 

[Mbear]

expansion vessel may have lost its full charge, isolate central heating cicuit at boiler feed and return, drain off excess pressure via prv and check pressure in expn vssl and recharge to manufacturers req pressure. open up heating circuit and recharge to working pressure (1 bar) and check that heating works ok and prv doesnt blow off again.

OP, do you really use the heating flow and returns to isolate boilers?
I know that's exactly what they are for but I don't dare use them ever. 99 times out of 100 they leak. I feel sometimes that I just look at them at they leak lol. The only time I'd ever consider using them is to prove a leak on the boiler or the system and even that would be a last resort

 

[oldplumber]

better than a full drain down and if they leak, replace them, after completing a full drain down after all its the customer paying and if something is broken it needs repairing

 

[kpp]

thanks guys something to work on
kev

 

[Mbear]

better than a full drain down and if they leak, replace them, after completing a full drain down after all its the customer paying and if something is broken it needs repairing

you don't have to do a full drain down If replacing combi water parts, just dump the pressure at the chb and work away.

Don't get me wrong I may take a chance on using them on an open system but on a combi system I'd just use the prv to dump the pressure and then replace the prv after if done my repair. I only carry one or two iso valves(vokera compact&mynute) so I'd rather get it all done in an hour-ish ,rather than go back the next day with new valves

 

[oldplumber]

never had a problem with isolating valves to date, each to his own in then

 

[moony]

never had a problem with isolating valves to date, each to his own in then

lucky lad then.

i have had problems and it can be a boiler off the wall jobby, combis are so easy to drain and refill i never use the valves.


mbear what do you mean by chb mate?

i drop pressure by prv and replace if necesary. but i drain down at lowest pont majority of time and refil with inhibitor 9 quid charge customer. they also like the fact im putting inhibitor in - peace of mind etc.

 

[Mbear]

lucky lad then.

i have had problems and it can be a boiler off the wall jobby, combis are so easy to drain and refill i never use the valves.


mbear what do you mean by chb mate?

i drop pressure by prv and replace if necesary. but i drain down at lowest pont majority of time and refil with inhibitor 9 quid charge customer. they also like the fact im putting inhibitor in - peace of mind etc.

chb - central heating boiler mate

Maybe the iso valve issue depends on which part of the uk you work in. But I can tell you this, in Glasgow it's not advisable to use the iso valves. Don't even look at them lol

 

[moony]

must be a celtic thing then cos here in wales the valves are dodgy too - thought it might be central heating boiler haha... just thought there prob be some other abbreviation someones brought up on here - have a hard time with the old abbreviations and text speak haha

 

[kpp]

thanks guys,
checked pressure in expansion vessel=nothing so pumped up to 1 bar, this made the pressure gauge increase and decrease when reduced. would this mean membrane is good or split? this would indicate the supply tube is clear although it does not get hot when the boiler reaches 3 bar and dumps, indicating a blockage?
regards kpp