Banging Pipes Just After System Turned Off

[jon_1978]

I have a S plan system, when the system gets hot and I turn it off the pump and boiler go off as you would expect, then system hot water shoots up the heating fill pipe into the header tank and the pipes bang for a couple of minutes. I have tried manually leaving the zone valves open so the water can flow but still the hot water in the system goes up into the header tank. When I turn the CH back on I can hear it filling and air bubbling into the radiators so have to bled again.

 

[ChrisR]

Boiler is?
Overun stat if fitted, may not be working.
Or the pump may not be wired from the boiler output.

 

[jon_1978]

Boiler is a Baxi WM 381 RS, by overrun stat do you mean on a bypass pipe incase the TRVs are all closed? I have no bypass pipe as I have only have 2 TRVs. I have tried manually leaving the zone valve open to allow flow. The pump and the boiler are wired together so they come on and off together. The system will run for hours and be fine its just when it goes off the water shoots off into the header tank.

 

[gas4you]

I think these boilers control the pump over run via the pcb, a common fault.

 

[jon_1978]

I have wired the system as the s-plan wiring on the following link.

http://content.honeywell.com/uk/homes/systems.htm

When the CH/HW goes off the pump and boiler switch off together and the zone valve closes.

The fill from the header tank is below the pump and the vent is just below that.

 

[gas4you]

If as I suggested the pump is controlled from the boiler then that wiring diagram is wrong.

Check to see if there is a pump live out on the boiler wiring terminal, if there is then this is where the pump live should be connected.

 

[jon_1978]

I have had a look and there's only one wire coming out the wiring terminal on the side of the boiler and on the information on the flip down panal it just says 240V input.