Am I being fobbed off by heating guy?

got gas central heating system updated but was left with knocking sounds in the radiators...got the guy out who fitted it. He says its just the pipes heating up/cooling off but I've kept the heating on for four solid hours and it's still knocking. Surely the pipes would be 'heated up' by now?

Sounds like more than heating up sounds. Lived with expansion-contraction sounds in a previous house but they didn't last that long. Also, was almost more sound when the heating was turned off in the cold than when it was turned on.

Not unusual to have knocking sounds - pipes under your floor are expanding and contracting

If you have thermostatic rad valves fitted at each rad you will find more knocking as the rad may go cooler until set point is reached and when it opens it sends the cooler water out to make noise. People with standard stat in the hall don't have this problem as the water is continuously circulating at a fairly constant temperature - ie they only get the knocking on startup or shut down.

ah yes, I did get thermostatic valaves fitted to all the rads. Thanks so much for clearing up mystery!

L