CRANE 100 series gas boiler hammering

Hi, I just moved into a home that has a CRANE 100 series gas boiler. Would any one out there have either a manual, or could give me advice on how to stop the hammering sound.

It did not hammer when we moved in. Then one day there was a smell of hot dust on the radiators (they got too hot) and the pressure relief value opened and release around 2 litres of water. I’ve both opened the intake water value to refill, but if I exceed 30lbs it releases pressure again. If it’s under 30 lbs it hammers. I have bleed all the radiators and they are full.

There is a device on the outgoing pipe that looks like it measures temperature (it has markings from 200 – 100). It is wired to be inbetween my thermostat and the boiler. Does anyone know what this is and what it does? I’m thinking that it prevents the boiler from becoming too hot, and it is not functioning, thus my system is overheating.

Thanks for anyone that can help me.

keith