Wocester Heatslave 20/25 No Power Blowing fuse

[aje9999]

Hi, Hope someone can help.
I have had the above boiler for 5 years.
On Thursday night I put the heating part on for first time in 4 months.
After a while I noticed only the first rads in the line had got warm and when I checked the boiler it was not running even though there was demand (It had not gone to Lockout). I tried tuning up both HW and CH thermostats but still boiler would not even try and fireup, no pump noise or anything. I did notice however that the boiler seemed quite hot inside but this is maybe right?
The follwing day after a bit of reading I pressed the reset button under the electrical panel, NOT the lockout button on the burner.
Hey Presto boiler fired up and we had HW and CH.

However this morning Saturday no HW again and when I checked the boiler there was no power light on, checked fuse in plug that was OK but the 250v 3.15 A on the electrical control box had blown.
I changed this fuse and power light comes on but as soon as you switch the HW or CH to come on the boiler goes to start but the fuse blows agian within 1/2 a secon after switching it on.

1)If anyone has any ideas on whats causing the fuse to blow I would be grateful ?

The only part that has been re[laced on this boiler from new is the small motor for the 3 way valve.

 

[aje9999]

Oh I just tried disconnecting the pump connector from the control board, when I do this the fuse does not blow and the boiler fires up ok when I switch HW on.

Could it be a new pump is what is needed it has never had one in 5 years?

 

[chrishutt]

Sounds like the pump. Has any water leaked onto it, perhaps from the Auto Air Vent? Can you test for resistance through the pump windings?

 

[aje9999]

Hi Chris,
Thanks for you help
Theres a bit of residue around the unions and on the back end of the pump where the 2 unions join into it but its definitley not wet and theres no trace of residue on the actual pump part itself.

I am thinking maybe its just worn out. I have a meter, but do you know waht sort of resistance readigns I should get?

Also do you know if I can just change the front bit of the pump ie undo the 4 screws that hold the pump to what I guess must be the impeller part wher the unions go into or do I have to undo the unions and replace the whole lot?

 

[chrishutt]

Pumps usually last a lot longer than 5 years. What make is it (Grundfos, Wilo)? You can remove the head part and replace (with cheaper CH pump) in most cases, but not all. Take a resistance reading and I'll tell you if it sounds right.

 

[aje9999]

Hi Chris,
Resistance readign I tookat the connector and reads 190 ohms.

The Pum says Bosch on it but then below that it says Grundfoss
Type UPS 15-60X18
pn 59526645 if that means anythinng to you.



I have to pop out for an hour so will be back asap

Thanks for all you help

 

[chrishutt]

190 Ohms sounds about right, so you need to check resistance to earth (should be infinity of course). The coils may be fine but shorting to earth due to water penetration. A standard Grundfos 15-60 pump (£40?) will provide a new head.

 

[aje9999]

Hi chris,

I`m back now had to get a belt for the hoover, not my weekend!

Right I went acroos the brown and the earth lead on the connector whcih is not plugged into the board by the way and again got 190 ohms if I go across the Neatral and the earth wire its infinity.

If I get just the back aprt of the pump, when I undo the 4 screws is it going to leak water?

Will I need to bleed/fill anything back up again or is it just a case of undoing the 4 screws removing the pump and diconecting the electrics to the pump unless there fixed and then replacing with new pump in reverse order?

 

[chrishutt]

You've obviously got leakage to earth, but why infinity between neutral and earth when both earth and neutral have 190 Ohms to live?

You'll have to isolate and drain the water from the pump before undoing the four screws. I can't describe all the procedures involved in draining/refilling 'cos I've spent enough time on this already. Unless someone else wants to take over you'll have to do some more research yourself.

 

[aje9999]

Ok Chris,

Thanks for your help, will get apump and try it.

 

[Agile]

Chris, either he has got muddled over what he is measuring ( more likely ) or there has been a serious trauma and the neutral winding is no longer connected to the neutral tag but instead shorted to earth!

The resistance will vary depending on the speed position selected but is usually between about 180 and 240 ohms.

If a Grunfoss pump has burnt itself then it produces a very distinctive smell which I always teach my trainees to recognise.

Many faulty pumps can test OK at low voltage but short when mains is applied.

A very simple way to check that is to power the pump from an external mains lead with a three amp fuse.

Tony

 

[aje9999]

Hi Tony,

Thanks for the advice. On furhter inspection there is a small flat seg type pice of metal that looks like some sort of screw in the union the pump goes into above the pump, this has asmall water leak coming from it, I think this is maybe what has damaged the pump. Think this is maybe some sort of vent that Chris referred to earlier but not sure.maybe

Anyhow I just got a new pump £61.50 the whole thing that screws intot he two union pipes not just the back part, if its possible to just get the back part that is.

Just need to find out what the leaky thing is, then repair it and then find out about the job of swapping the pump out, need to pluck up some courage for that though.

Thanks again for your advice its really appreciated.
Adrian

 

[chrishutt]

Adrian, the things you describe either side of the pump are isolating valves. You close them by turning the screwdriver slot 90°. This may or may not cure the leak! If it doesn't you should replace the whole valve - easy to get for a couple of quid (sounds like you may have new ones with your overpriced pump) - but you'll need to drain the system to do that.

When the pump is isolated via the valves you can go ahead and undo the head screws. A little water will leak out (catch with rag).

 

[aje9999]

Hi Chris,

There doesn`t appear to be any screwdriver slot inthem to turn.
The one thats leaking is like a rectangle in shape but curved on either end.
If their meant to be turned it would need to be done with pliers or mole grips. Tried to upload a pic of what I mean but cant see how to upload pics.

 

[chrishutt]

Is it like this? If the leak is from just above the gland nut, just tighten it. To close the valves use an adjustable spanner (not pliers, etc.) on the flats of the square and turn fully clockwise.