Apollo 40B banging boiler

[DIYMike]

Please help ....

My Apollo Boiler & pipework is making banging noises when the heating thermostat switches off. The pump stops and the boiler flame goes out when the stat switches. I have already changed the High/Low stat but the problem persists. I have chemically cleaned and dosed the central heating system. I also added Fernox noise silencer. The gas valve also locks out and shuts off the pilot light on occasion when the central heating stat or hot water cylinder stat switch off. The grunfos pump is under a year old and is in the high speed setting. The 3-way valve is working fine and all the rads are working ok.

I'm not sure if the boiler has a pump overrun stat or not
Should I clean the system again
Please help.

Regards
DIYMike

 

[kevplumb]

I'm not sure if the boiler has a pump overrun stat or not


yes it does

Pump Overrun Thermostat - Thermodisc 60T13-500073

 

[DIYMike]

Kevplumb

thanks for the fast reply

If the pump is switching off at the same time as the boiler flames off - does this mean the stat is faulty? Should the pump continue running for a while

 

[kevplumb]

yes its a low water content boiler as soon as the flow stops there is enough resibual heat there to boil it