Overflowing F & E Tank All aspects of plumbing questions and answers, help, tips and information

[one arm bandit]

My problem is the F & E tank overflows when the heating is turned on. The system is a floor mounted Potterton gas boiler situated downstairs with an indirect cylinder situated upstairs. It is gravity feed with no motorised valves. The cold water supply tank with the F & E tank are situated in the loft area. This problem started recently and only occurs when the heating is turned on. The indirect cylinder has been installed for 31 years. The boiler was replaced 10 years ago. Any suggestions as to why this is happening. Alan in Welling.

[Dave From Leeds]

Alan,

I think the key here might be the age of the cylinder. It may be that the heating coil inside the cylinder has perforated, allowing water from the HW system to be drawn into the primary circuit which is fed from the F&E tank. The only solution to to that particular problem is a new cylinder.

Does it happen if you run your system on Hot Water Only?

[one arm bandit]

Thanks Dave, you have confirmed my suspicions and no it doesn't happen when HW only is on. Now trying to locate indirect cylinder with imperial dimensions between the primaries i.e. a straight swap if I'm lucky.

[Dave From Leeds]

Alan, before you go running off getting a new cylinder, there's another possible cause, given what you say here:

" no it doesn't happen when HW only is on."

It may still be the cylinder coil but that the hole in the coil is so small that it's only when the pump is running that water is drawn into the suction side of the CH circulation.

Alternatively, it may just be that something has changed within the CH system and you have a phenomenon known as "overpumping". I believe this would manifest itself as water being pumped up into the F&E tank through the vent pipe over the top of the tank, whereas with a perforated coil the extra water would be likely to enter the F&E tank through the bottom. May be worth checking. If it's overpumping it may be possible to eliminate it by slowing the pump down. Mine has 3 speed settings.

Please bear in mind that I am not a plumber, just a keen DIYer with a bit of expertise at problem solving by logical elimination due to a troubleshooting type job that I had for 20+ years.