Simple explanations for plumbing problems

Constantly running overflow – coil in an unvented cylinder pin holed

The customer had been struggling with a overflow running constantly for a few weeks.  Several attempts had been made to identify the fault. The ball valve had been changed, the water level in the tank had been adjusted, the open vent had been checked to make sure it wasn’t pumping over.  Finally the mains supply to the cylinder was turned off overnight.  When they got up in the morning the overflow wasn’t running. The only remaining cause of this (in this case) is the coil in the cylinder having a hole in it. This lets water at mains pressure mix with heating system water at much lower pressure causing the system to overfill and the tank to overflow. Sadly the only solution (I think) is to replace the cylinder. Ive been told that in the good old days they used to get a flexible piece of copper pipe and shove it through the coil.  But I don’t think that would work with more modern coils as they have tighter, higher efficiency coils.

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