My central heating boiler went on the blink, which is a problem because we had no hot water. Luckily we have a contract with a company so I was able to call them out. I thought it was the timer because the heating was not kicking in when the timer moved round to ‘on’. But no, the nice man from the company could hear the pump kicking in but the flame was not lighting. So he had a look and removed this, it’s a solenoid. Basically the circuit has to close to light the boiler so that the heating comes on its apparently worked by electromagnetism. I’m really pleased he fixed it. My boiler is twenty five and still works well. I’m worried that it is going to become obsolete. Hopefully they will be able to get parts for a few more years yet…..