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back boiler fault

Postby bittybunny » Mon Mar 29, 2010 7:33 pm

hi guys got a problem with a back boiler,dont know which model but is mated to a robinson willey fire,back boiler is controlled by a randall hot water only or heating and hot water timer,in hot water only mode the hot water flows and returns through the hot water cylinder circs just fine,in heating and hot water mode the radiators get very hot ,but the flow circ to the hot water cylinder gets boiling hot and the return is lukewarm,the heat is so hot through the flow to the hot water cylinder it is going all the way back up to the header tank and filling it up via the 15mm heating system filling pipe,whats the most likely problem,thanks and kind regards,rob gas safe gas engineer
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Simply Build It

Postby htg engineer » Tue Mar 30, 2010 7:09 pm

Could be a faulty boiler stat, with the CH on the pump will get rid of the heat via the rads, with HW only on the heat will struggle to escape via the 28mm pipe and will vent over.


A blockage in the cylinder coil, with the CH on the pump will push the heat through, but when on HW only there's no pressure to force the water round.

Faulty stat is most likely as you say the radiators get very hot.

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