Not knowing too much about the inner workings of these, do I assume
correctly that there is some kind of flow switch inside that fires up the
burner when it detects the cold water tape running? Guessing there is also
thermostat in there somewhere.
Over the past month, it's got steadily worse from whereby messing about
turning the tape on/off got it to fire up to really not working at all.
CH side seems fine.
The OP has not said what make and model of combi he has. There are 3 or
maybe 4 different ways the boiler might detect the water flow.
If the CH is working then the fault most likely rests with the flow
detector (or PCB just maybe). The diverter valve is unlikely to alter
whether the gas lights when a tap goes on.
Just for completeness here are some of the mechanisms that I know of.
1) Differential pressure on a venturi acts on a diaphragm which moves
2) Nozzle acts on a paddle connected to a microswitch.
3) Flow drives a small turbine to give out electrical pulses.
4) Differential pressure cause by the hydraulic resistance through the
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
There is a bank of lights on the combi itself showing pilot light, burner on
etc. What sometimes happens when the tap turns on is that the lights all
light up to the top (top is ignititoin) I think but then fall back down to
just below "burner running" light.
If that helps :-)
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