Boiler fuses blowing -Vokera Excell 80SP

[jack_s]

The fuses (2A internal PCB & 3A external fuse) on my boiler have started blowing occasionally again, after about 9 months.

The boiler is a Vokera Excell 80SP.

When blown fuses are replaced the boiler runs ok.

Internal PCB fuse first blew in July 2004, then Oct 2005.
In Jan 2006 both internal PCB fuse & external boiler fuse blew at same time.

Now in Oct 2006, the internal PCB fuse blew once, followed by external 3A boiler fuse blowing 3 times each after 5 day period.

Any ideas why bolier runs ok for period then fuses are blowing ??

 

[jack_s]

Any ideas ??

 

[Agile]

It may be a water leak onto an electrical component.

Pumps have a tendency to give intermittent shorts and then recover.

So do 230v ac suppression components!

If you are competent you could wire the pump into a seperate supply with a 3 A fuse.

As its only very infrequent I would be inclined to fit a new 1A quick blow fuse in series with the pump supply lead.

Tony

 

[jack_s]

It may be a water leak onto an electrical component.

Pumps have a tendency to give intermittent shorts and then recover.
So do 230v ac suppression components!

If you are competent you could wire the pump into a seperate supply with a 3 A fuse.
As its only very infrequent I would be inclined to fit a new 1A quick blow fuse in series with the pump supply lead.

Tony

I haven't seen a water leak in the boiler.
The boiler is in an outside shed, so I wondered whether the problem may be caused by humidity/dampness.

Is the pump only used for central heating circulation ??
I haven't used heating for long while, only tap hot water.

I think a fan runs constantly.

The fuses have blown themselves, without seemingly being linked to me using tap hot water
(or heating, which I haven't used for long while).

Jack S.

 

[Agile]

Sorry to disappoint you but fuses do not "blow themselves".

The current carrying conducter ruptures when the current exceeds the rating by about 30% typically.

Something in your boiler is causing an overload !

The pump is used in both DHW and CH modes.

Tony

 

[jack_s]

Sorry to disappoint you but fuses do not "blow themselves".

Something in your boiler is causing an overload !

The pump is used in both DHW and CH modes.

ie: the fuses don't blow due to my action (switching on hot water tap) but due to boiler fault.

At random times I go to switch on hot water tap & no hot water.
Find fuse blown not seemingly triggered by me switching on hot water tap.

I thought pump only circulated hot water in central heating.
Is it pumping water to hot water tap ??

Jack S.

 

[Gasguru]

May be worth checking/replacing the fan resistor. Its the high wattage resisitor screwed to the combustion chamber on the right hand side. Sometimes they can short to earth via the casing.

 

[jack_s]

May be worth checking/replacing the fan resistor. Its the high wattage resisitor screwed to the combustion chamber on the right hand side. Sometimes they can short to earth via the casing.

No fuses have blown since I posted last October.

Finally getting round to looking at this, as the 3A external plug fuses have started blowing again (7 fuses in a row).
Think they may blow when it's damp weather conditions.

Think you may be right about it being related to fan.
Replaced fuse, switch on, hear gurgling sound & fan runs for a second, then bang as shorts somewhere on boiler, fuse blows.
Did this 7 times (fault has never repeated itself like this before one after other).

Boiler is running ok for now, but will look at the fan resistor.

Thanks
Jack_S

 

[jack_s]

Just realised the fan was replaced in 2002 after some water entered boiler (maybe through flue).
The fuses often blow when first switching on boiler.

Could fan be faulty with high startup current ??

Thanks
Jack_S

 

[DP]

Fan runs all the time, so there is no high start up current.

Anyhow, the fan is 47 watt. A two amp fuse would supply some 500 watts of power. Cannot see the fan drawing 500 watts.

What is I see suspect is boiler location and fan being changed (later in the thread).

Suggest you get a tester and check insulation in mains components- no point in poking and hoping. Do not alter/ modify the internal wiring.

 

[jack_s]

Fan runs all the time, so there is no high start up current.

Anyhow, the fan is 47 watt. A two amp fuse would supply some 500 watts of power. Cannot see the fan drawing 500 watts.

What is I see suspect is boiler location and fan being changed (later in the thread).

Suggest you get a tester and check insulation in mains components- no point in poking and hoping. Do not alter/ modify the internal wiring.

See my post just above on 29 Mar.

This time the 3A External fuses have been blowing (the fuse in wall plug that supplies boiler).
The fuses have blown 1-2 sec after switching on power, when fan is starting up (motors have higher currents at startup).

As fuses were blowing on power-up when fan was starting, thought it could be dodgy fan causing problem.

But normally I just replace fuse & it runs ok.

Thanks
Jack_S

 

[DP]

Remote diagnosis is impossible. One can only speculate on causes which often prove wrong.

Now consider the following. Your boiler is out in the open damp atmosphere (be it under cover). The fan has also been replaced as water ingress through flue had knackered it. If water enters the combustion chamber through the flue, there is a good chance it will spill onto the PCB housing (after the combustion chamber is flooded). As I have stated above, it is all speculation. You want facts, get the testmeter out and check insulation.

Fan motor is high up- any water ingress is unlikely to effect the coil as water will run down not up. More chance of water running down onto some other electrical connections and popping the fuse.

At start up/ idle no demand state, 560 ohm resistance will limit the fan motor current to less than 500 mA (even with motor short circuited)

 

[ChrisR]

Have a good sniff around, literally. You can often smell toasted insulation!
Running a separate lead can help diagnosis,

 

[jack_s]

Have a good sniff around, literally. You can often smell toasted insulation!
Running a separate lead can help diagnosis,

What do you mean running a separate lead ??

Jack_S

 

[jack_s]

Have a good sniff around, literally. You can often smell toasted insulation!
Running a separate lead can help diagnosis,

What do you mean running a separate lead ??

Jack_S