DIY Doctor UK DIY Forums

The Boiler does not always come on immediately when you turn on the thermostat on the wall. When the boiler does eventually come on it only stays on for a maximum of 3minutes then stays off for a couple of minutes before coming back on - during which time the light on the thermostat remains on.- A new pump has been fitted and is working ok. this problem has been ongoing. We have now replaced one of the radiators since doing so all the upstairs radiators are 'Hot' and working ok and only one of the radiators downstairs is working- Please help

This sounds like a system fault. The boiler is being controlled on/off through its thermastat for short periods indicating the heated water is not being moved quick enough. Try to find out if a by-pass has been fitted in the pipework, close to the boiler.
If you close all the upstair radiators and leave the downstairs ones on you may be able to encourage movement in lower part pipework and possibly shift any air trapped.