The boiler expansion emits boiling water to the outside. The control panel has been replaced and then the pump. The problem is very intermitent, say 3 or 4 times a week, remainder of the time perfect. There are no airlocks in the system. I am retired but experienced with boilers but on this occasion I have run out of ideas

John Heighway, June 2008

odd one , but a couple of suggestions. Is the level in the jockey tank too high ? do you have trv's on the rads ,if so is it y plan or s plan. check and see if you have a bypass fitted. if you have an auto bypass this may need to be re-set. is the water dirty? you may need to put in a system cleanser , but if you try this make sure drain as appropriate. good luck

Kieran, July 2008

I have said the Boiler above is a Ptteron Prima when it actual fact it is a Potterton Primera

John Heighway, June 2008

Thank you for your suggestions but the Primera Boiler is not a combi or presurised boiler but a fully pumped system. I was when working a fully qualified electrician and the system is definately wired correctly. The new pump runs as it should its supply comning from the boiler panel also havoing overrun facilities which again work perfectly. HELP

John Heighway, June 2008

sounds like a problem with the expansion vessel, whats the system pressure like when cold then again when hot?

make sure the expansion vessel is charged, and not leaking from the valve (if it is leaking at valve, it will have to be replaced)

reasons for water through safety valve would be the water pressure has exceeded 3bar, make sure system pressure when cold is 1- 1.5 bar, if thats ok, monitior it when heating is on, if it then exceeds about 2.5 bar, it points to the expansion vessel either faulty or undercharged.

Also, if system pressure is going up and down when cold over a period of time, your filling loop may be passing water (hence your system pressure wil tend to go up when mains water pressure does (higher at nighttime when water demand is low)

let me know how you get on

T, June 2008