Replacement PCB 5111603

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I have just installed the above in a Potterton Suprima 60, but it keeps blowing the main 3amp fuse in the electrcial supply spur after abovce 20 seconds. I have checked the mains wiring onto the terminal block and also onto the PCB both OK.
I know the next stage is to check for shorts on Pump, Fan & Gas Value, but how do you do this? These were OK before PCB was replaced. I have also checked the the PCB fuse but cannot see if this needs replacing.
Can anybody help me?
 
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you would have to guess that one of the wires is either going to the wrong connection or touching something it shouldn't. To check the resistance on the pump and fan first electrically isolate them and then measure the ohms reading across live and neutral...tell us what you got. Basic electrical checks will pick up a short.
 
If you can't use a meter to test the pcb fuse I don't think you should be going in there. As you are though, for gawds sake turn the gas off while you're testing. Then get someone qualified to turn it back on.
 
why replace pcb, :?:
try replacing old pcb, :?:
was new pcb a recondition unit, had some baxi pcb's that blew the main fuse after 20 secs think it was on the new model 100he/barcelona so it may be a batch of faulty pcb
 
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If it was blowing the fuse before aswell then your problem may well be down to a faulty flow switch.....there was a faulty batch early 2003
 
Thanks for the advise:-
all wires OK and free from body of boiler casing.
Ohms readings; pump 0.19 and Fan 0.05.

PCB replaced because the old one was locking out. The cylinder stat would call for heat, boiler light and go out after less than a minute. Had an engineer call after I had not used the boiler for a week. Boiler was OK he could not find a fault but said this type of boiler had many PCB's fail so he suggested I replace PCB. So I bought a new one.
The old PCB did not blow any fases.
Just for the sake of it I reconnected the main and pump supply wires.
The light flashed red three times and then fuse blew.

++++++++++++++++++++++++

I have just re installed the old pcb but it also blew the fuse.
Any further advise?
 
I have just re installed the old pcb but it also blew the fuse.
Any further advise?
 
Your lack of knowledge is alarming. You could easily leave something dangerous. Call a heating engineer.
 
Hi, Thanks for the advise.
Got a heating engineer to look at the pcb/boiler and controls, He checked the boiler, fuses kept on blowing out.

He checked both the room stat and HW stat. Both OK. eventually he by past the programmer to fire the boiler and said I would need a new programmer.

Brought a new pragrammer, this also blew the fuse(3A). However I was unable to by pass the programmer the way the engineer had with out tripping the 13A trip on the main electric comsumer unit. So I spoke to the Heating Engineer, he suggusted I get an electrican to check out all the controls.

So on Wednesday that is what I did. He checked out all the controls, well I think he did, the only items that blew the fuse(3A) were both the myson MPE 233 valves. So I bought new Actuators and installed these today and guess what they blew the fuse.

Do not understand why the boiler will not fire up and also why the fuse keeps on blowing!
 
Your "heating engineer" does not seem to have been very competent!

I would expect anybody using that title to be totally experienced with electrics and a fair degree of electronics. After all thats what modern boilers run on!

I do hope he operated a "no fix-no fee"!

Tony Glazier
 
you won't need to bridge the programmer to check its operation, just test resistances on the clock pins...bridging out the clock won't prove a fault. It won't be the valves that blow the fuse but they are sending a signal on to a component which is.....check the pump again, or disconnect it briefly and see if the fuse still blows. Don't take this the wrong way but my guess is that its been wired up incorrectly.
 
I have disconnected the pump but the fuse still blew.

The wire to each component was checked by the electrican as being OK.

I have double checked this, it appears to be wired to a typical Potterton Central Heating and Hot water Zone Valves terminal Connection Diagram.
 
You cannot assume that testing with a pocket meter at LV will find a fault!

Many pump faults only occur with mains voltage applied and need to be tested at 500v with a Megger or similar.

A DIY method to test the pump is to independently wire it to a plug fitted with a 3 A fuse and leave it running for an hour or so.

However in your case if the fuse still blew with the pump disconnected it seems that the fault is somewhere else. Perhaps a fault in a cable rather than in a unit?

Now is it blowing via the neutral or the earth ??? Knowing that would help to find it !

Tony Glazier
 
Thanks Tony,

Pump OK being running for an hour.

The orange cables from the MPE 222 are connected into the wiring box but where does that cable go to. According to the schematic wiring diagram it should be connected to the SWL on the boiler. Is this correct as my installation has no cable there.

How do I test to see if the fuse blows via neutral or the earth?

I am sorry if these questions seem basic to you.
 

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