How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Plumberpro Your Own Question
Plumberpro
Plumberpro, Plumber
Category: Home Improvement
Satisfied Customers: 634
Experience:  Fully qualified plumbing , heating and gas engineer 20 years experience
77408428
Type Your Home Improvement Question Here...
Plumberpro is online now
Home Improvement
This answer was rated:

Baxi Solo HE boiler does not modulate in response to boiler

control knob?
Ask Your Own Home Improvement Question
Hi . did you get a change in ohms value on temperature change , with the thermistor?
Customer reply replied 3 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 reply replied 3 years ago.

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

Ok
Customer reply replied 3 years ago.

Thermistor resistance reduces with temperature increase.

Ok , then that's working . does the boiler temp get too high.?
Customer reply replied 3 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 reply replied 3 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.