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Discuss Intermittent Overheat lockout on a Worcester Heatslave 25/32 circa 2007 in the Oil and Solid Fuel Forum area at

  1. Wag

    Wag New Member

    I have an intermittent overheat issue (every 5-10 days) with a Worcester Heatslave 25/32. According to the customer the Dhw becomes scalding hot and the boiler then locks out on the overheat stat. So it’s locking out on the hot water side presumably. There are no external controls on the hot water and the boiler has been linked out from fitting, the heating is controlled by a 2 wire Honeywell digital Programmable stat.
    Looks as though the wiring is correct although I have had to Rewire the frost stat as the switched live back was wired directly into the switched live from the Programmable stat not the fs connection.
    I have been on the line to Worcester and they have had me change the hot water and boiler stats, then the Pcb, and then the pump. The issue persists! They cannot think of any reason why the stats would continue a demand for stored hot water after the demand is satisfied.
    Is there, in your opinion, any reason to change either the flow switch or the diverter head? I’ve checked the Microswitch is not jammed and that the flow switch is working normally. As the issue can occur at any time of day or night (most recently 6 in the morning) before any taps have been used or any heating demand is switched on I have to assume that a normal topping up of the Heat Bank occurs and then for whatever reason the burner doesn’t switch off.
    Any insight would be appreciated
  2. Vee

    Vee Plumber GSR

    I would wire in a return stat with the Frost stat to stop overheating should the Frost stat activate.
  3. SimonG

    SimonG Trusted Plumber Top Contributor!!

    Would have said sticking relay on pub. Or there's a leak/drip on the hot water pipework
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