baxi 100e



the fuse on the board keeps blowing every time i turn it on i know it can be the gas valve or fan or pump. how can i test these with no electric to pump or fan the fuse on the pcb blows stright away.
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Don't know how to say this without it sounding a bit daft, but how about disconnecting the gas valve?

Have had a hi limit thermostat leak to earth enough to blow the fuse, so you could go the other way and disconnect everything, adding back until the fuse blows. Only uses the one fuse, hopefully!

You can test thigs with an ordinary meter of course, though thinks like insulation breadowns might not show at low voltage so you'd need the expensive sparky's/Part P tool. Any sign of a leak on the pump?
It cannot be the gas valve because that is not powered until after the fan has started.

Why not disconnect the fan and see if it allows the pump to run?

Or better still disconnect the pump and power it from a seperate plug with a 3A fuse.

It could be a part on the main PCB faulty. I had one on a Suprima pcb.

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I agree Gaz that its probably the PCB but you have a Potty one in your van whereas BOB has to go out to buy a non returnable one so he has to be 100% sure first !

Exactly. As I said
"you could go the other way and disconnect everything, adding back until the fuse blows". If the pcb by itself blows the fuse, it would tend to be indicative!

Be careful about assuming that say, eg, the gas valve isn't the culprit because it wouldn't come on yet, unless you're sure of how it's wired. Quite often they switch things in the NEUTRAL, so a leak to earth would still blow the fuse before it would normally start working.
i will try the resistance on pump and fan and gas valve i know thew pump is about 334ohms does anyone know what the fan and the valve are
DOn't know for the specific boiler but
Fan will be somewhere about 35 - 100 ohms(R) typ 50R
Gas valve 500 - 5000 , typ 1k4, 2k8 coils
Pump typ 160R for a 6m, so more for a 5m, ok.

Live - E for each should be off the scale high end.
If its blowing a fuse its more likely to be a short to earth.

That might not be measurable on a LV test as it is usually a breakdown at 230 v

just an update on boiler i whent to boiler and removed the wires to pump
and there was only 37 ohms resistance changed pump now ok
I think we can assume that the pump was faulty!

If BOB had followed my suggestion on the 2 nd Sept it would have been fixed much earlier.

( That was to externally power the pump from a mains socket! )

but surely not as simple as just checking the pump resistance.
A typical pump resistance is about 160-220 ohms. With winding to earth greater than 2,000,000 ohms.

But many pumps break down to earth with 230 vac applied to them although when they test as normal with a LV tester.

Supplying them from an external 230v source is a quick and easy way to confirm them as faulty or working.

But that costs a fuse! Now we're all Part P enabled we just get the "Megger" out!

(Or sniff the thing)
The Megger will only measure the resistance to earth at 500v or 1000v.

There can be a fault condition with a breakdown from live to neutral when 230v is applied.

Sacrificing a 10p fuse is insifnificant when I am charging £1 a minute!

Tony Glazier

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