my boiler runs ok for DHW had new divertor valve last year and flushed. CH starts runs for 20 mins, rads get hot all ok, then boiler starts hissing banging. Checked pump was running by undoing screw on front and its stopped.If i leave boiler off to cool down for 20-30 mins it then it starts again ok but soon after pump will stop again.

Rod, November 2007

I have had same problem. It sounds like you may need new DHW/CH temp sensors; (potterton no:430011), as well as You may need a new pump if it has been damaged when jammed.
The DHW/CH thermostats may also need replacing, if the water is too hot.(nos:929562/929634).
I have used the 'Rated tradesmen' internet site to get reliable tradesmen in the past if you don't know a reliable heating engineer. Best of luck.

Jay, January 2008