We have water overflowing from our header tank when the DHW is on.
The water (hot) comes up the expansion pipe on the primary circuit, and over into the header tank, which then overflows outside. Slow dripping, not a gush. The header tank gets reasonably hot while this is happening.
Turning the thermostat down on the tank, and hence stopping the boiler, immediately stops the flow, as you'd expect.
Suspecting a faulty Cylinder stat, I've just replaced it, but it's made no difference....
So, any ideas ?
If the coil in the cylinder was split, it would be overflowing up the cylinder vent, not the primary circuit vent, and doing that all the time, so I can't see it being that, but could the cylinder coil be stuffed up with gunge, and so not letting much of a flow through ?
Any other possibilities ?
The boiler is a (20+ year old) floorstanding potterton. Open vented CH and DHW system, the cylinder looks about 10-15 years old I guess - it's got yellow bonded on foam insulation, so it's not absolutely ancient.
The water (hot) comes up the expansion pipe on the primary circuit, and over into the header tank, which then overflows outside. Slow dripping, not a gush. The header tank gets reasonably hot while this is happening.
Turning the thermostat down on the tank, and hence stopping the boiler, immediately stops the flow, as you'd expect.
Suspecting a faulty Cylinder stat, I've just replaced it, but it's made no difference....
So, any ideas ?
If the coil in the cylinder was split, it would be overflowing up the cylinder vent, not the primary circuit vent, and doing that all the time, so I can't see it being that, but could the cylinder coil be stuffed up with gunge, and so not letting much of a flow through ?
Any other possibilities ?
The boiler is a (20+ year old) floorstanding potterton. Open vented CH and DHW system, the cylinder looks about 10-15 years old I guess - it's got yellow bonded on foam insulation, so it's not absolutely ancient.
