What other info do you require?
Serial No.is: N019580804 GB
G.C. No.: 47-970-17
Does that explain the low gas pressure when HW selected?
Thank you for the further explanation. One more question. Could it possibly be caused by dirt in the pump? You suggest that water would heat up too quickly if heat exchanger blocked but water at tap never gets above warm.
Good question It being summer the heating hasn't been used for weeks. It was switched on briefly for a check of that very thing but only until heat was felt at the nearest radiator. That check, of course, does not prove that CH is working properly.
I'm afraid that isn't possible as the boiler is in my daughter's flat, some distance from here. OK, and finally I hope, if it is the heat exchanger that is u/s would the temperature gauge on the boiler shoot up before the burners switch off?
Thanks for the info. It gives more things to examine tomorrow morning.