I have a normal boiler (non-combi) that is 2 years old in a fully pumped
open vented system, with a programmer and a thermostat in the hall. The pump
is 1 year old.



I switched off the heating for a week to go on holiday and since switching
it back on I have had difficulty getting the heating to come on. The hot
water is fine (comes on regularly) and the boiler fires up for that, but the
heating has only come on once or twice in the last few weeks. The pump is
very hot and I can hear it fizzing/gurgling but no central heating.



The system has been flushed recently and I recently rebalanced the radiators
as the living room radiator (the one furthest from the pump) was only luke
warm with the one nearest was scorching.



Any ideas?