Ravenheat combi-boiler 82et -----HELP------

[pavickers]

My parents have the above boiler, a few months ago the heating and hotwater just went, this was repaired by changing the diamphram in the 3 way valve. Everything has been fine until now. Since last week the hot water has virtually stopped working. The 3 way valve is making the microswitch and the burner lights up on full for about 20 seconds, then everything goes off, and the water starts to run cold again. Any idea what i should be looking at, my thoughts so far are 1. the potentiometer or the DHW sensor.. Thanks in advance

[gucciman]

first thought would be the hot water thermister. failing that then its possibly due to the water not circulating thru the boiler correctly so the heat is building up and the thermostat is then cutting the burner off, could be down to a blocked heat exchanger or the pump not functioning correctly. could be down to the circuit board. could be the diverter valve still, if we have a problem with one then we change the whole valve, not just the diaphragm

[gucciman]

first thought would be the hot water thermister. failing that then its possibly due to the water not circulating thru the boiler correctly so the heat is building up and the thermostat is then cutting the burner off, could be down to a blocked heat exchanger or the pump not functioning correctly. could be down to the circuit board. could be the diverter valve still, if we have a problem with one then we change the whole valve, not just the diaphragm.
if you live anywhere near brum give me a shout and we can fix it for you.