Nest migration - Worcester-Bosch CDi pump problem.
I thought it was something to do with Tado as I hadn’t had the problem with my Nest and logged a support call. It seems no-one else reported this and all my wiring of Tado checked out ok.
So my Brother in law disconnected all Tado/Nest wiring and switched boiler back on and pump continued to run… so must be a boiler problem. On researching several Worcester-Bosch plumbing forums he found others had this problem and someone posted the solution which we tried and so far it’s working ok again with my new Tado installed.
Posted solution below - no idea why these boilers have this glitch.
Cheers
Mike
“Every time the boiler is turned off at the mains or there is a power cut, after about a min or so, the pump runs, and it runs forever (the burners are not on in this time). During this time if i run a tap or turn on heating it works but afterwards the pump continues to run... forever.
However, I have discovered if a hot tap is running or if the heating is on (and thermostat set to on) before the boiler is turned on at the mains and then turned off a few seconds after the burners start then the pump will stop after its normal over run of a min or so and then stay off. They boiler will then function as normal.”
Comments
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This depends on the way your system is wired. Modern systems have something called 'pump overrun' which means that the boiler itself controls the pump 'live'. This is so that when the boiler shuts down (assuming no power cut) the boiler will instruct the pump to run on longer, to cool the boiler. The boiler will then cut the power to the pump itself. The alternative wiring is for the pump and boiler to always live at the same time, via a jumper between the two connections. Either way, the boiler is switched on when either the hot water valve or the heating zone valve is switched on (assuming an S plan install). So really, this is nothing whatsoever to do with tado, which doesn't have control directly over the pump. I have a Worcester Bosch 24Ri, and this pump overrun works fine. So it sounds like you have a problem with your boiler - either the wiring or the circuitry inside. Given your 'fix' I have a vague feeling you may have an issue with a zone valve - perhaps the switch inside is sticky or something? I'm not a professional, so I would seek help from a good engineer if I were you.
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He has a combi boiler, so that doesn’t really apply.
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I have an old Bosch Worcester Greenstar HE & I have also read that my pump will run continuously but I haven’t noticed anything running. Would it be obvious to me if it was running, what sound am I likely to hear?0
