Combo boiler heating when thermostat is off; Plumbers Forums

Combo boiler heating on when off issue

I have an Oil Firebird 70 Combi boiler. When the thermostat is off, the rads warm up (upstairs mostly) whenever I turn on hot water tap or whenever the boiler comes on periodically to keep its internal water reservoir hot (for instant hot water). I’ve disconnected the house thermostat just incase it was faulty. But same problem.

I was expecting to find a 3 way diverter valve. But can’t see it. Anyone know what I should check in my boiler from this pic? Also read that these Firebird boilers don’t have a diverter valve.. Thanks

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