We have (I think) a gravity fed, vented, indirect hot water system that works along side a immersion system with two heating elements for use with economy 7. Age is approx 18-20 years.
The HW/CH system seems to work OK.
I want to use the immersions to heat in the summer while the heating is off. However the immersion heaters are not heating the water.
Given both had failed, I checked the controller and found a blown electrolytic capacitor on the controller board. I replaced the controller with a new unit but I am still not getting any heat from the elements.
I have checked the power (Don't panic, I have experience of working with HT supplies!) and it appears that power is getting to the elements and that the thermostats are working correctly.
I suspect that, when the old controller failed, the elements may have been left heating indefinitely and permanently (limited only by the thermostat).
Finally to my question: Is it possible to find out if both elements have blown by testing their resistance? Basic maths says that a 3kW element should have a 20 ohm resistance, but I do not know if that still applied when the element is cold.
Alternative question: Am I missing something simple? Is there another possible solution?