My 28i boiler runs even when turned off at the timer or the thermostat is set to zero. When faulty it runs full speed / full heat and we have to turn it off at the boiler. This is an intermitant fault. Worcester came out to it and it ran fine for 3 days. I would say it is a sticking relay but I doubt it has any. Any suggestions ?

Glyn Mellor, November 2009

if all external controls working o.k, could be flow switch sticking or faulty inbuilt frost stat

mark, November 2009