Cheers! Tell you what was happening!, the system was updated by a prevoius plumber (my sisters house, boiler changed just before they moved in) looks like a floor standing cast iron heat exchanger boiler was taken out and the ferroli low water content boiler fitted. Its got part copper pipe work, from new boiler to old steel pipes to most of the rads. The vent and feed pipes were both on the positive side of the pump which caused major pumping over to the expansion tank!! Also all rads were sludged up and varous leaks were found on old compression joints!
The prob they had was after the boiler had been on for a good hour it would make a loud banging and flushing sound, but not every time. After lots of invstigating and guessing, i came to conclusion that it was prob pumipng over and sludged up worse than i thought, so altered system for expansion and feed where on negative side of pump before boiler and manually flushed out system and they replaced every rad (12 off em!) along with a flushing agent and a system inhibitor added after.
Still it did the same, but they noticed it was everytime the boiler shut down after running for a least an hour, or when it had reached max temp.
On shut down, programer would close the valve with then closed the pump and boiler at the same time. After about 2 to 5 minutes when everything was still off (pump, boiler and zone valves shut) thats when you could hear the water boiling and rushing up the pipes and out of the open vent pipe into the tank!!!
Realised then that the boiler (copper low water content heat exch) was still heating water and boiling it !
Why hasn't this boiler got pump over facility already installed ??
Its fan flued and has a Pcb, so would expext it to????
Took me 2 weeks to find the problam out!!
Not the normal CH fault.
So thats why i needed to know if could add a pump over circuit fitted !!!
cheers!!
