We recently had a problem with our oil-fired boiler. For the 2 days it was off, we relied on the immersion heater for hot water. This has not been used for a couple of years at least.
Central heating is a sealed pressurised system whilst the hot water vents into the cold water storage tank. When the boiler is running, we have no problems at all. There is a cylinder thermostat linked to the boiler However, when we use the immersion heater, we get boiling hot water and also hot water coming out of the cold bathroom taps.
I suspect that the thermostat on the immersion heater has therefore packed up and hot water is venting into the cold water tank.
My questions therefore are:
1. Is my diagnosis likely to be correct or could there be another cause.
2. Assuming it is correct, will this necessarily require a completely new immersion heater.
Any guidance gratefully received. Thanks
Central heating is a sealed pressurised system whilst the hot water vents into the cold water storage tank. When the boiler is running, we have no problems at all. There is a cylinder thermostat linked to the boiler However, when we use the immersion heater, we get boiling hot water and also hot water coming out of the cold bathroom taps.
I suspect that the thermostat on the immersion heater has therefore packed up and hot water is venting into the cold water tank.
My questions therefore are:
1. Is my diagnosis likely to be correct or could there be another cause.
2. Assuming it is correct, will this necessarily require a completely new immersion heater.
Any guidance gratefully received. Thanks
they now have stats that offer more protection ( fail-safe) than old ones.....Loosen it with the system full of water/in working condition ( with the flex disconnected) then drain some water + remove....there are plenty of bent cylinders from doing it other ways 
