Tony - many thanks for that.
You could be right about the flow rate. The pump was replaced only a few years ago but the problem is worse with only the c/h circuit (micro-bore) on by itself. If I add in the h/w it improves a little (though still not satisfactory imo).
The thermostat...
I have a 20yr old Ideal Gas c/h boiler model 50N which takes ages to switch on again after top temperature reached. Thought I'd replace the boiler thermostat. Bit worried by the boiler end of it. There's a fixing pin across the opening the probe disappears into. Do I simply remove this pin...
