Radiators getting warm when boiler is on over run

[mike71]

about 9 months ago, my glowworm boiler was replaced by a new worcester bosch unit. At the same time, the system was flushed, fernox protection was added, new 3 way valve and the bypass pipe with gate valve was replaced by a auto bypass. i dont have any TRV valves on the rads. Ive recently noticed that all the radiators get a little warm when the boiler stops supplying heat to the hot water tank (heating is permanently off) and the boiler is simply doing its 3 minute over run. I didnt get this warming condition in the rads with the old glowworm. Is this normal do you think or something is wrong? Thanks

 

[ShaunCorbs]

It’s dumping the extra heat in the boiler to prolong the life of the heat exchanger

My honest opinion 3 ways don’t need an auto bypass (does this get warm when it does the 3 minutes cycle ?

 

[mike71]

It’s dumping the extra heat in the boiler to prolong the life of the heat exchanger

My honest opinion 3 ways don’t need an auto bypass (does this get warm when it does the 3 minutes cycle ?

Hello Shaun, Ive investigated further. Both sides of the auto bypass are hot in all situations. I guess its set at the lowest pressure. Before this autobypass was fitted (a few months ago with the new boiler), it was simply a pipe between flow and return with a gate valve. this gate valve was always open. What Ive just noticed is when the boiler stops sending heat to the tank and it starts its 3 minute over run, i can hear the 3 way valve clicking a few times and i can instantly feel hot water now starting to flow through the 22mm pipe into the central heating system. Obviously, this is why my rads are getting warm during the 3 min overrun. Makes me wonder whether the 3 way valve is wired up wrong. A new one was installed at same time as the new boiler was fitted. I never had this warm radiator issue with the old glowworm boiler.