On Sun, 28 Dec 2003 13:45:53 +0000, Rik Smithies wrote:

Another thought, I live in a soft water area (Birmingham), so is this
scaling still a likely explanation ?

OK so we are not looking at limescale but the same effect could be had
by debris build up on either the primary or secondary side of the heat
exchanger.
Or you might have a normally working boiler but the temperature sensor has
drifted out of spec.
Or the thermostat board inside the die-cast box - middle horizontal board
has a problem.

To progress further you will need to see if the gas is cutting because the
primary flow temperature has gotten to 80-90C (bad 2ndary HE) or because
the sensor/PCB is over enthusiatic.

Another possibility is that the modulator on the gas valve has failed, you
can check to see if that might be the case by looking closely at the
flames to see if they reduce before the gas gets cut.

HTH

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html