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Discuss NEST - Help with heat link/thermostat in the Central Heating Forum area at UKPlumbersForums.co.uk.

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  1. Keith Rann

    Keith Rann New Member

    Hi guys, I wonder if someone can help me with an issue I’ve been having with my Nest controlled central heating system.



    Basically, when installed (3 years ago) the system worked perfectly for a good year or two until a fault appeared and occasionally the central heating would not turn off – creating a tropical climate in my living room! As mentioned this fault was only on an occasion, I spoke with a Nest advisor and we did some tests which they put down to a faulty unit and a new one was issued. This seemed to resolve the issue temporarily but the fault reappeared.



    This time the unit was now out of warranty and the Nest advisor suggested the relay in the Heat Link was faulty and not turning the boiler off (hence why the heating system continued running). Fast forward a few months and I bit the bullet and purchased a new Nest system (about 2 weeks ago). The exact same fault within a few hours of installing!! Nest support hasn’t been great in identifying the fault so I thought I would seek further guidance for where I can go next?



    Basically, when turning the thermostat to demand heat you can hear the relay in the Heat Link switching on and off, it appears that when the heating system is on for a good hour or so the relay can be heard switching off but oddly the boiler etc. doesn’t stop. I have done a continuity test on the Heat Link and if you switch the heating on and off quickly the voltage goes to 235v on demand and down to 0v when you turn the heating off. However, like mentioned when you put the heating on for an hour or so, the voltage goes to 235v and stays at 235v when you turn the heating off even though you hear the relay noise – baffling me now!


    Sorry for the long-winded post… hope someone can help?
     
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Where's your boiler ? Do you have a frost stat ?
     
  3. Keith Rann

    Keith Rann New Member

    I have a potterton conventional boiler, not sure about a frost stat. Is this something I could easily check - the boiler was installed approx. 1992/1993.
     
  4. Keith Rann

    Keith Rann New Member

    The boiler is in a 1st floor cupboard with the hot water tank. The Heat link is approx. 500mm from the tank and boiler.
     
  5. Joe50

    Joe50 New Member

    I had a similar problem when I switched to Nest thermostatic control I found that the CH control valve would hang on and not de-energise, when switched off by the Nest thus keeping the boiler on via the valves integral contacts. It's easy to check if this is happening with your installation by using the related Nest smartphone app. To fix, I wired a neon across the Nest output to dissipate any residual voltage in the output circuit. I just happened to have some neon indicators in the garage, but any additional load like a resistor or similar across the Nest output should work.
     
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