potterton suprima 100 failing fan ?

[mcother]

can anybody please give me some advice on this problem please
i had the pcb and fan replaced 14 mnths ago now the boiler will run for about 3/4 hr before the fan will not start it will try but it seems as there is not enough ompth in it .if i take the cover of and spin the motor it will work for another 1/2 hr or so i have tried another new fan and this does the same can the pcb be at fault again or is it the big capacitor adjacent to the pcb. any help pleeease!!!!

 

[engineer]

potterton have modified the pcb and if your boiler is pre week33 1998 it will have a sifan fan with capacitor this must be changed if pcb replaced or capaciton will blow pcb if replacing both you will need a harness kit (5113950)

 

[Agile]

We assume you had the old style PCB and fan fitted.

From what you say it does sound as if the capacitor may have failed or lost some of its capitance.

You really need to measure the capacitance and see if it agrees with the marked value. I dont know about your fan but motor start caps are usually between 4 uF and about 10 uF.

Tony Glazier

 

[croydoncorgi]

Come on Tony! How many people know how to measure capacitance?

Anyway - I believe the story so far is as follows:

If you had the PCB AND fan replaced 14 months ago you SHOULD have got the new-style PCB (card-cage, wiring etc.) which has some possibility of reliability - unlike the previous (at least) 9 versions of essentially the same rubbish PCB!

Some Suprimas (I think 100s and 120s but maybe smaller ones too) used to have a fan that required a starter capacitor and would not work without one. However, the latest PCB etc., is AIUI NOT compatible with the old motor.

So when the PCB was updated the fan should have been changed too - and apparently was.

But the new type of fan does NOT require a starter capacitor.

You can easily tell which fan type you have: the old cap-start type has an EXTERNAL rotor (a large green or black-painted thing that goes round). The new type has an INTERNAL rotor which is quite small and mostly hidden inside the motor body.

Do NOT try and run the fan with a defective capacitor - it'll overheat and burn out. The new cap is relatively cheap. A new motor is not!

But if you eventually need another new PCB (if you've still got the old type, you will), you'll need a new fan too.

Maybe our resident Potty expert will confirm my facts and dates.

 

[mcother]

thanks for the advice chaps it has the old sifan fan and pcb in it i have ordered the new capacitor anyway and hopefully this will cure the problem if not i suppose its time to change the fan and pcb for the newer version i will post any further news as soon as the new part arrives .
thanks again

 

[Agile]

John, I can measure capacitance and inductance, so can Chris 1 DH and I would not be surprised if you can do so too!

Whilst both Chris and I have an expensive Megger LCR meter, my current trainee bought a nice meter on special offer at Maplin with capacitance AND temperature for about £12 !

Tony

 

[croydoncorgi]

Yes Tony - I know YOU can.
And yes - my meter also has capacitor test sockets. But I wonder whether it would cope with the large value, electrolytic starter cap in question. And I'd have to disconnect the thing to test it.
All in all, given the symptoms and the lack of alternative culprits - just change the thing would be my advice!

 

[lor]

we would apreciate if you would explain how to test a capacitor for us that dont know

thanks alot

 

[Agile]

AC mains voltage capacitors are not electrolytic types as those are only suitable for DC. They are normally metalised foil construction.

Even the cheap £12 meter my trainee bought has a capacitance range of 20uF and so that would be ideal for measuring motor start caps.

To measure a motor start cap you need to disconnect just one lead but join them together first before connecting them to you meter in case they have any charge ( many motor start caps have a built in discharge resistor though ). Then set you meter to a suitable range to measure 1-20 uF and read it off!

Tony

 

[ChrisR]

I also have a meter I bought for £2.20 which measures 20uF and temperature. Cheap because it had no leads! (Temp probes are cheap too at Maplin)

Also ordinary ch pump capacitors are worth checking if you think the pump might be going slow. One day I'll do some tests with different value caps to measure how the speed is affected. That requires a rev counter, from £10-20 up (can also be used on fans).