Peculiar central heating problem - any ideas?

[paul1001]

Our central heating system "bangs" sometimes when the Hot Water comes on. A single bang.

The engineer came and replaced the mid valve actuator. This had no effect. The engineer came back and replaced the mid valve. This seems to have had no effect.

We have a recording taken on my iphone when the hot water came on. The noise is like a shot fired in the cupboard which reverberates along the pipes. (I haven't figured out how to upload it.) You can hear the bang after hearing the mechanism starting up the hot water.

During the winter we never noticed any banging except the times when we turned on the hot water for a mid day boost while the radiator heating was off. Before the last engineer visit, we experimented by turning the thermostat way up just before the hot water came on. When we do this we have never got a bang.

So what could be the cause? Anyone any ideas??

 

[ShaunCorbs]

Could be the coil in the cylinder do you have a valve on the return ?

 

[SJB060685]

There was a similar problem a while back, i believe it was the mid position valve. There a different types (internally) and one of those types was causing the problem.