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Plumberpro, Plumber
Category: Home Improvement
Satisfied Customers: 634
Experience:  Fully qualified plumbing , heating and gas engineer 20 years experience
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Baxi Solo HE boiler does not modulate in response to boiler

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Baxi Solo HE boiler does not modulate in response to boiler control knob?
Hi . did you get a change in ohms value on temperature change , with the thermistor?
Customer: replied 2 years ago.

Hi. did not check.

The value should change with temp difference. Try in cold water then hot water , should be different ,if not then sensors faulty .
Customer: replied 2 years ago.

I will check your suggestion immediately & get back to you.

Customer: replied 2 years ago.

Thermistor resistance reduces with temperature increase.

Ok , then that's working . does the boiler temp get too high.?
Customer: replied 2 years ago.

I suspect it does as hot water is ejected from the expansion pipe into the header tank.

The last time I had that happen the pump wasnt running and had to be replaced as the water was sitting in the boiler and boiling over . it could be a problem with the pump
Customer: replied 2 years ago.

I suspected the pump but discounted it as it is less than 12 months old & outwardly appears to be moving water. I cannot see why a faulty pump affects the boilers temperature control?

The burner fires at a rate which relies on water moving through the boiler at a certain rate, if too slow it will heat up more than designed for. If they pump isn't too old then you may have a blockage in the pipes , air scale or sludge. . if the pipe work is very old then it could be blocked . you may need a flush or at worst a change of flow and return pipework from boiler up to motorised valves and back . but check if there are any manual air release valve in the cylinder cupboard.
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