My feeder tank for the central heating has started to overflow, this appears to have a vent pipe I assume from the cylinder. I have isolated the feed to the ballcock, to ensure this wasn't dripping in. There is another open ended pipe feeding into this tank. I am not sure what this is but assume it some form of relief fromt he cylinder, can anyone point me in the right direction,
There will be two vent pipes in your roof. The one of the CWST comes from the cylinder. The one over the F&E tank comes from the primary circuit.
It sounds as though you are experiencing "pumping over". It could be due to any one of a number of factors:
1. CH Pump Speed Too High
Try turning it down and see what that does. Note this will only be a temporary solution.
2. Blockage In Pipework
Needs flushing out if it's sludge or if it's a magnetite deposit it'll probably need that section of pipe cutting out and replacing. I'm afraid you'll need a professional for this.
3. Feed and Expansion Configuration Incorrect
Low chance of this if it's a recent occurence but if so needs to be fixed.
4. Vent Pipe Too Low
Needs to be raised.
5. Boiler Stat Set Too High or Gone
The water coming out of the vent pipe is only a symptom and not the problem. It's important that this is fixed because all you are potentially doing is drawing aerated water back into the system which causes more corrosion which causes more sludge and also wastes a vast amount of heat and fuel.
Whatever the answer is you are going to have to get someone in to look at it for you. This isn't a DIY thing if you don't know what you are doing.
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