Hot water problems

[mfgs]

Just had a phone call about a sabre 25he. Apparently the heating is fine, but the hot water keeps going hot and cold and is impossible to run a bath or have a shower. Although the kitchen hot tap which the customer says is only a couple meters from the boiler isnt affected by the problem. I'm thinking thermistor or blocked plate? Any other suggestions, anyone had the same problem on this boiler?

 

[Simon F]

if the tap closest to the boiler runs without a problem, then does it not suggest a restriction in the pipe runs to other taps causing the boiler to cut out because of getting to hot?
does the pump have a speed switch, has it been turned down?

 

[mfgs]

I did ask if the flow to the taps was ok, they said it was the same as always but it just runs hot then cold and hot again. So I am guessing the burner is dropping out as it thinks its up to temp. I havnt been there yet, just want to be armed with as much info as possible before going there in the morning.