Combi boiler heating circuit overfill

by **collymac** » Sun Dec 30, 2007 10:10 pm

My 18 month old SABRE 24 combi boilers pressure gauge constantly rises ( up to 2.7 bar ) resulting in the relief valve dripping (this can take an hour or two ).The filling loop is disconnected ruling out a passing valve.When i turn off the cold main at the boiler ( leaving me with no hot water ) the problem stops & after draining slighlty i can have the heating back to normal .Any ideas folks

by **htg engineer** » Mon Dec 31, 2007 11:05 am

If the problem definately stops with the cold water turned off then it could be the plate heat-ex is corroded.

2.7 bar is abit low for the pressure relief valve to open - its normally 3.5 4.0bar - so you may also need a new pressure relief valve.

by **collymac** » Mon Dec 31, 2007 1:08 pm

sounds like good advice ,it was a cheaper price boiler so i'll not be surprised if corrosion is the problem ( true saying , you get what you pay for ) I'll check out both the relief valve & the heat exchanger .thanks for your help & Happy New Year

by **roger196** » Mon Dec 31, 2007 6:37 pm

Definitely a leak between the cold water side and the CH side, most likely culprit is the heat exchanger. Check the manufacturer's instructions for fault finding charts for other possible leakage spots eg across the diverter valve.
Pressure relief valve usually set to lift at 3 bar, but again check manufs specs. If a cheap boiler, the pressure gauge may not be that accurate in its reading. Its much safer for valve to lift early rather than at too high a pressure.