Loft Header Tank

Hi, My small loft header tank in the loft is overflowing when the hot water/heating is switched on. It’s fine when the heating/water are off, but starts up again when it comes on again. It started with a few drips a few weeks ago to a slow flow now, which lasts for about 10-15 minutes when the heating/water initially comes on and then stops dripping again. Any ideas?

Asked by Justin on 12th Apr 2021
Expert Trade Answers
Best Answer
"Hello it is quite possible that this is caused due too known as pump over this occurs when then circulation pump speed is set t maximum speed if it turned down to 1 or 2 this should stop the pump over occurring"
Answered on 13th Apr 2021 - Member since Mar 2021 - report
"Water overflowing from the small feed and expansion tank can sometimes be quite sinister if its constant and can signify a problem with your hot water cylinder. Given the issue is intermittent I would say you only need a new washer or float operated valve replacing within the tank itself. Here's what's happening:

When the heating and hot water is off the water level in your tank sinks down as a result of the cooler water being of less volume than hot water. This allows the float valve to drop which allows water to enter the tank. The water level in the tank only needs to be very low. If the float valve is faulty it will still allow water to very slowly enter the tank which would normally take quite some time to reach the overflow level and lead to a visible drip from the overflow pipe. However, when the heating/hot water is switched on, the water in the system expands and causes a sudden rise in the level of water which exits the overflow pipe. The initial overflow then reduces to a drip until the heating is switched off again, whereupon the cycle starts again.

Water is very interesting in terms of its properties in that it expands when it gets hot but also expands when it freezes."
Answered on 19th May 2022 - Member since May 2022 - report
"Hi there, is it an old system and have you had a new pump fitted? The pump could be set too high or fitted wrong."
Answered on 12th Apr 2021 - Member since Sep 2019 - report
"Hello, check central heating pump if in circulation, close it. Looks like to be blockage in the system or faulty pump."
Answered on 12th Apr 2021 - Member since Mar 2018 - report
"This is called “pumping over” usually means vent pipe needs to be higher, increased in size or you have a blockage."
Answered on 13th Apr 2021 - Member since Mar 2021 - report
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