How to diagnose & repair a motorised heating valve

Solving motorised valve problems: In this video, Roger explains how a motorised valve works and discusses how you can easily diagnose and repair a motorised valve, avoiding the need to buy a costly replacement.

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About Roger Bisby

Roger Bisby
Roger Bisby is an English television presenter and journalist, known for his expertise in the British building industry.


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    Interesting video. Just one point: you mentioned that those motors are brushless and therefore you don’t understand why they burn out. An honest admission, so l’ll explain. An electric motor does not require brushes in order to burn out. If the motor is forced to draw too much current (in this case probably by excessive mechanical resistance in the valve mechanism) then the windings will overheat and are likely to eventually develop an open circuit failure. Result – motor has burnt out. No brushes involved!


    Chris (electrical engineer MIEE, ret’d).

    • Roger Bisby

      Thank you for taking the trouble to explain. I have taken those motors apart to try and understand what is happening. The valve stays open by the continuous force of the motor so that would be the excessive current draw. What I don’t fully grasp is why some motors are happy to do that for 20 years while others fail. There are no visible signs of burn out. No smell either. I am going to look up Synchron and see if I can understand.

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    Hi Roger,

    Thanks for the very informative video. I was excited to try out the manual override on my HW diverter to see if it got the boiler firing but no joy still. Boiler fires when CH is turned on only. Checked thermostats too. With CH on and HW on manual I can feel the hot water entering the tank but if I stop the CH the boiler stops even though HW demand still on. Is it still likely a diverter problem? I always like to try myself before calling a pro (within reason of course) at least to ensure it’s not something basic. Thanks for your time.

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