Potterton Profile Prima 80 NG Air Pressure Switch

[Olive Splitter]

Any ideas on all of this?

Boiler not firing - exhaust fan running no ignition spark or gas - the suspect pressure switch was replaced with a genuine brand new part - still the same problem.

Pressure switch triggered with a screwdriver releasing the micro switch - everything now works fine - release screwdriver but boiler keeps on running up to operating temperature then will not cycle back on - fan not even running - wait a few minutes pull off clear pipe at bottom of switch (with restrictor) fan now runs but no spark or gas put pipe back on - still the same fan on but nothing else happening.

Pressure and vacuum pipes blown out and inspected for leaks - both ends visually inspected nothing wrong found.

Pipes not kinked in back of controls section new pipes (controls section) fitted - no joy.

Restrictor (0.25mm) is clear - no joy.

Stripped down entire flue - went at heat exchanger with flue scraper from above - every single slot cleared - all seals and gaskets OK - still no joy. So for once looked at Potterton Fault finding Chart for boiler which having tested for "240v between T2 & T4 on electronic control" with multi meter found no voltage - so chart then said - check pressure tubes and check or replace air pressure switch. Still the same problem.

Can see straight through the flue to the outside nothing wrong flue clear - outside area around flue is clear

Restrictor removed boiler fine on old original pressure switch and old pipes - fit 0.34mm restrictor (was other restrictor in kit P/N 909030 with pressure tube replacement kit - new design).

Boiler now running perfectly on 0.34mm restrictor and old switch - but will not run on correct 0.25mm restrictor.

BUT Two days later boiler not running AGAIN - remove the restrictor (0.34mm restrictor is totally spotless and can easily see light through 0.34 pinhole) - boiler now running perfectly without any restrictor and cycling fine.

Boiler had new genuine Potterton exhaust fan by EBM/Papst Germany on 04/12/2010 - runs very quietly and spins fast.

How is it possible for the boiler to work perfectly for two days on 0.34mm restrictor then stop again? What changed in those two days?

What else to do if it stops again without any restrictor? What else causes these symptoms?

 

[mountainman]

Still sounds like an APS problem, if you maintain that the APS is good then maybe the fan is intermittently running slow.
There is really not that much to go wrong in this boiler.

 

[bennygas]

hate to say it, but I've had similar problems with these in the past. found my solution by chance - knocked bottom tray holding pcb and it sprung into life - apparent dry jointing on pcb.

 

[Olive Splitter]

Thank you for your replies.

Update - This morning the boiler stopped running again - pressed in APS black (presumably natural rubber) diaphragm gently with screwdriver - boiler fired and water came out of APS diaphragm next to the micro switch actuator - which proves APS diaphragm was finished as it has a hole in it (which can’t be right!) and am certain was gentle enough with blunt screwdriver that I did not make the hole – wear and tear from age did - fair enough.

New APS put back yet again (translucent blue diaphragm the [synthetic? silicone?] rubber will probably prove even more durable in use), with new clear hose and the correct 0.25mm restrictor (not a new one but a new design one that was already in use – the old style long one that used to join and restrict the original two clear pipe assembly will remain retired from use) anti kink springs installed over hose – the heat exchanger scraping probably also helped.

Boiler now again working and cycling correctly - for the moment - all closed up and waiting to see if a permanent fix this time - mountain man you are correct APS diaphragm had hole in it re water - bennygas if PCB responds to being jolted or jarred will have a good solder up of dry joints the moment the PCB gives me the excuse – is that how these PCB’s normally fail - dry joints - or is it generally obviously failed/charred components?

Have also discovered from all this that the correct restrictor stops excess movement of air in the sensing pipes which will contain condensation from boiler combustion gas which will then condense into acidic water flood any APS new or old and the water logging of APS will cause APS diaphragm to not move and boiler to stop – is my guess correct?

If boiler keeps running intend to replace remaining red pipe in controls section as well as the two rubber pipes at the top that connect the flue elbow sensing pipes to the pair of alloy hard lines that run from control area at bottom to flue at top to head off any more porous/hardened/softened hose failure issues and improve reliability – does anyone have any other suggestions for minor parts they would replace on this boiler before they conk out and / or become no longer available?

 

[bennygas]

water in the aps is never right, it simply aint supposed to be there, so i would guess that's a big hint as to the solution to your problem. see how it runs mate. all being well it was just the aps. if condensation is getting into this assy it could well explain the failing operation over time, and why the restrictor works ok one day and not the next.condense gets in there again, i think you need to be trying to figure out why it's getting in there, and make sure you're using the right restrictor - it's there for a reason (I'm not saying you haven't, mind you). if wouldn't go tapping pcb case or anything unless you get a problem - if it aint broke don't fix it.