my sime 120 combi ,is working fine for central heating but hot water goes from hot to cold aprox every 3/4 minutes therefore can not run a bath or have a complete shower any ideas why? boiler tech does not know and sime telephone is uncontactable
What you need is a Quattro diverter valve it would take too long to explain the workings of the device but it will solve your problem cost approx £95 and extra cost for fitting if you are unable to do so yourself.
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Try fixfault.com to fix home heating systems.