My CH fan was running but it was not firing up, kept cycling for over 40 minutes before starting up and heating the house. To keep my dearest happy last night I reset the programme timer for an hour earlier to compensate, but it wouldn't heat up at all, just the fan noise, hummmm whoooosshhhh click silence, (or could have had click somewhere else in the sequence)repeated and repeated.

I read the thread http://www.howtomendit.com/answers.php?id=26383
got a recon PCB 407677 and fitted it expecting miracles and loads of brownie points.

When I reconnected the power nothing happened, no fan start up no hummmmwhoooshhhh no clicks. Its very cold tonight!!!

I would be eternally grateful if anyone any suggestions about how to fix this problem?

Blue nose Paul, December 2008

Earlier, at the start of this saga, Peccavi wrote...

"Are you certain that all the connections are correct on the new PCB and that heat is being called for?"

I am pleased your heating is now repaired - who says the young are useless? And they don't gloat either...

Uriah Heep, December 2008

The final chapter....

I rang a help line (which shall remain anonymous) and explained my situation and the rather nice chap at the other end of the phone went through what the readings should be for the various connections on the pcb. When I gave him the reading for the fan connections he said the fan was kaput. I took it to the recon establishment who were really helpful, put it on a test rig and said well while the bearings were a bit naff, you won't get any more speed and therefore air flow out of a new or recon one. Go away and refit the old one, but check the APS, 'cos that's my bet on where the problem is.

So I did what I was told and refitted the fan, but I am getting a bit desperate, 'cos it's coming to the end of the third day without central heating. Checked the APS and it was clicking fine - oh a useful tip from the recon people was that there may be a pin hole in the diaphragm, to gently blow across or down the tube, get the faint click of the APS actuating, then stick your tongue over the tube to hold the pressure for at least ten seconds. If it clicks while your tongue is over the end of the tube there is a pin hole in the diaphragm, but if it clicks after you take you tongue off the tube then the diaphragm is ok. As I said the APS tested ok.

I am very lucky in that my son who is away at college has two mates who are plumbers. Now why didn't he get them to do this in the first place you may say.. Well I'm a stubborn old s** and try to work things out myself, but when I'm beat I give up so I called them.

They popped round at 6.00pm tonight and at 6.05 the heating was back on.

When I removed or refitted the pcb I had pushed one of the temperature control spade connectors almost but not quite off the contact, so a glance at it looked ok but it wasn't connected. A good look at it would have solved the problem. Mind you they had to contort and twist themselves a lot to get a view because of the boiler position, but that's no excuse I’m sorry to say I missed a loose connection.

Thanks to everyone who commented and I hope that this is a salutary lesson. Check all the contacts are properly made or you may be wondering around for days going nowhere like I did.

And that's the story and tomorrow we should have heat and morning glory.

Blue nose Paul, December 2008

I took the pcb back and the guy I got it from and he put a second replacement pcb on a test reg which showed that the fan was comming on, I could hear the relay click in and then the clicks to ignite the burner. So I saw it being tested.

So I refitted the second recon pcb and the fan stays off, nothing happens. So I'm back to the potterton fault finding chart which says "Ensure 240v between L & N and SwL and N". Borrowed a multimeter and there is power there 243v.

"Has overheat thermostat operated?" I've tried pressing the reset button, but it seems to have no spring in it it's just sort of loose, push it up and it just drops down again.

Could this be the problem? Does anyone know what the reset button is supposed to feel like?

I hope it is, because the next instruction is "check all appliances wiring and electrical components"! which I don't know where to start, and after that it's "check there is 240v between T2 and T6" and there's nothing there.

buckley_p@o2.co.uk, December 2008

Iain,

Pretty sure I got the neutral in the correct place - second right on the terminal block, took photo, and have wiring diagram, belt and braces!

Have taken the recon pcb out, sprayed all the terminals with detoxit (electrical contact cleaner) replaced the board, and tried again, no joy.

Will return the pcb tomorrow am and ask for a new (recon) one. Maybe I'll get my old one back reconned!!

Thanks a lot for the advice

Blue nosed Paul, December 2008

your original fault was def the pcb and i believe alot of people call it hunting??? The fan spins in bursts not long enough to point to aps failure. Ive heard its down to resistors or capicitors before reading the above post but obviuosly we just change the pcb old for new, no comebacks or if they do...warranty.

you cant really go wrong with wiring, you got neutral wired in correct?

could the recon board be duff?

iain, December 2008

Hi Peccavi,

Thanks for such a quick response, yes you're right the fan was running, but we got no heat anyway so we're just as cold as before!

The old PCB was exchanged for the new (recon) one, so I can't put it back in.

I was very careful to put the connections back in the same places, both of the terminal blocks, and the 5 "loose" ones. Unless I've done something stooopid.

I am not sure how to find out if heat is being called for. I did nothing else to the system except change the PCB, and you are right again the fan isn't running now.

I'll try shorting out the APS but which of the three do I short to which, would it be T4 to T5 on the PCB terminal block?

Hope that all makes sense

Blue nose Paul, December 2008

At least the old PCB had the fan running when heat was called for - Perhaps you could put it back in.

Are you certain that all the connections are correct on the new PCB and that heat is being called for?

The sequence I believe is - Fan Runs - Pressure switch senses fan running (reduction in pressure) - The pilot lights - Then flame failure senses pilot alight - Then main gas valve opens. Heat glorious heat.

Your previous fault points to pressure switch, or the old PCB failing to recognise/act on signal from pressure switch. OR - Fault in igniter / gas valve to pilot - can you see or hear the igniter spark?

If the pilot igniter is not cracking you might be able to eliminate the pressure switch as a diagnostic/temporary solution by shorting it out - a jumper across the terminals - take care. Also examine solder joints on old PCB and consider replacing the capacitors as per previous answer you mention - see how pictures here...
http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler
Good luck...

Peccavi, December 2008