ChatterBank2 mins ago
hot water cylinder thermostat
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No best answer has yet been selected by italiancat. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.You should have a programmer with two seperate channels for heating and hot water. Either channel when switched on will independantly activate via the thermostats the motorised valve/s to open the boiler flow to the required demand and then switch on the pump and boiler.
The heating should operate independently of the hot water control unless an activating syncronmotor has failed leaving a valve open or the wiring is incorrect.
You probably need a heating control specialist, where are you in the country?
italiancat, Reading your detailed explanation of the problem, I think that you may have a fully pumped "y" plan system. This is a system that has a mid position valve some where on the system that will send the heated water from the boiler to either the cylinder , or the heating system ( both at the same time,if both are calling for heat ).An electrical/control fault has occured on the heating side, resulting in heating only being provided when you are asking for hot water, i.e. the cylinder stat at a reasonably high setting ( 60 deg. ).
Of course , I could be way off the mark assuming this, but this is one of the things your heating engineer will check out, because, as stanley man says, you will probably need the services of a competant heating engineer who is fully conversant with all types of controls.
Good luck.