Potterton Performa 28 Combi : Cyclic Starting - Stopping

Having had a Potterton Lynx combi that gave virtually trouble-free service for 12 years I replaced it about 4 years ago with a Potterton Performa 28. The Performa has been nothing but aggravation and excessive cost for the last couple of years having had a boiler engineer in to replace the push-rod seals and diaphragms on the diverter valve twice, a leaking DHW sensor, and a u/s air pressure switch.
Recently, no matter what I set the CH control to it only delivered lukewarm water to the rads. Rather than spend more money on getting in a boiler man again I thought the most likely cause was a partially blocked filter on the CH return isolating valve and removed and cleaned it. It was partially blocked with sludge but not enough to reduce the flow drastically. Anyway I put it back and reset the boiler and it worked fine. However, as I closed the dropdown front fascia panel the boiler shutdown and when I reset it again the fan and the pump start the boiler ignites but it shuts down within about 2 seconds. It doesn’t lockout but simply repeats this cyclic starting-stopping continuously until I switch it off.
It was frosty last night and this morning and I need it sorted fast. Any ideas what’s wrong and how to fix ?

i think your system needs a good flush through and an inhibitor adding as the smallist amount of debris or gunge can cause problems with heat exchangers, this can cycle the boilers.

When taking the case on or off you may have knocked an earth wire connected near the burner to the circuit board. the earth wire detects flame rectification and tells the boiler that the burner is on.

The mother board (PCB) with send an AC electrical current through the ignition lead as soon and fan and pump operate, this current then causes a spark at the main burner which lights the boiler. While ther burner is alight the PCB board continues to send the current though the flame which changes this AC current into a direct current and back onto the burner. The PCB board then detects the direct current via the earth wire and keeps the burner lit. If it does not get this current then the PCB board thinks the burner has not lit and starts the cycle again and again.

sloppytom said:

i think your system needs a good flush through and an inhibitor adding as the smallist amount of debris or gunge can cause problems with heat exchangers, this can cycle the boilers.

When taking the case on or off you may have knocked an earth wire connected near the burner to the circuit board. the earth wire detects flame rectification and tells the boiler that the burner is on.

The mother board (PCB) with send an AC electrical current through the ignition lead as soon and fan and pump operate, this current then causes a spark at the main burner which lights the boiler. While ther burner is alight the PCB board continues to send the current though the flame which changes this AC current into a direct current and back onto the burner. The PCB board then detects the direct current via the earth wire and keeps the burner lit. If it does not get this current then the PCB board thinks the burner has not lit and starts the cycle again and again.

Click to expand...

I would assume from the op post that HW is ok. Is the potentiometer moving on the PCB and not snapped?

Many thanks Sloppytom & Gas2Air for your fast responses. Thought I’d give you some detailed feedback below.

The DHW was working fine when I was just getting lukewarm CH which is why I thought the CH filter was blocked and cleaned it. One extra thing I’ve now remembered is that at that time I don’t think the boiler was modulating, i.e. it was firing-out full heat and then shutting down, then firing-up again about 3 minutes later and belting-out full heat and shutting down again. This was making the pump very hot but the rads were only lukewarm.

After the cyclic stopping / starting problem I first thought I must have broken a cable connection although I hadn’t realised the significance of the earth return to the pcb described by Sloppytom. I thoroughly checked all the connections to the pcb and others that were accessible but couldn’t fond any broken or loose. Also took out and inspected the pcb for dry joints, burnt components, etc, but couldn’t spot anything obvious.

Yesterday was the coldest day of the winter so far (in London) so, with no CH or DHW, I bit the bullet this morning and bought a new pcb based on the premise that before the boiler failed the flames weren’t modulating implicating the pcb or gas valve. I was also influenced by other posts on this forum commenting on the dodgy pcb’s fitted to Performa’s and that the pcb design and part number (now 5112380) had been modified since mine was made.

Fitting the new pcb (now made by Honeywell and a better-looking board than the original) was a bit confusing since the connector locations have been moved around and the pin numbers reversed which bunches-up the cables and makes the pcb plastic cover even more difficult to refit. Also, the new board has an extra flying earth lead that I terminated on a spare earth connector close to the pcb.

Anyway, I’ve reset the boiler and its working fine in all respects giving piping hot CH & DHW and modulating nicely so I’m sure it was the old pcb that had failed. I’ll still thoroughly clean out and inhibit the CH system as suggested but which cleaning / inhibitor products do you recommend?

One thing I’ve noticed each time this boiler has failed is that almost all its components are made in Italy and I presume that this is where Potterton / Baxi source their boilers from now.
This and the unreliability of this boiler has persuaded me that I will not be buying Potterton / Baxi again since my experience in the offshore oil and gas design industry is that we have more quality problems with Italian manufactured equipment than any other (apart from Chinese). I certainly regret changing my reliable old UK-made Potterton Lynx for this Perform junk.
The problem is finding out where boilers are made these days before you buy them – you certainly can’t tell by the ‘manufacturers’ name on the boiler!
And before anybody suggests buying German 'quality' boilers, my neighbour is on the point of dumping a 3 year old Vaillant because of a failed heat exchanger which would cost over £300 to replace - he's already had a diverter valve and a temperature sensor replaced in the last year. He's spitting feathers and as fed-up with Vaillant as I am with Potterton!

I like to use fernox, or salamander.

I find worcester are most reliable but they are owed by a german company now. and the most expensive. there junior ranges are good or the britishgas 532 is an awesume boiler

Glowworm make vaillants now and are assemble in belper derbyshire.
i like the flexicom ranges.

Baxi are good on there solo/duo tech ranges, cheapest.

i stay away from the italian boilers.