My Potterton Performa 24 has developed a DHW fault, & I need help resolving it please.
In November, it stopped producing hot water and heating, & had a new divertor valve diaphragm and a new PGB fitted. All was fine for a while.
Recently however, when using hot water, the flow is luke-warm at best. When turning on the tap, the boiler ignites for 15 seconds, then switches off for 11. Then on for 15 seconds, off for 11. And so-on. The water supply temp goes from (very) briefly hot, to arctic, and back and forth. Having scoured the internet for a remedy, I've read several possible causes, as follows: Faulty thermistor. Divertor valve actuator. Divertor valve microswitch. Circuitboard or loom. Heat exchanger. DHW sensor.
While the hot tap is on, the l/hand 22mm pipe becomes hot, which tells me the divertor valve is sticking, but why is the boiler going on & off at those regular intervals?.
Assuming that the divertor is the cause, do I need to change the entire divertor assembly or just the actuator?
As you no-doubt know by now, I'm pretty bad at fault diagnosis so any & all help would be greatly appreciated, many thanks.

Simon Earl, April 2014

Ok thanks. Is it easy to access, being at the back?

Simon, April 2014

you need to check that the plate 2 plate heat exchanger is not blocked up with sludge from the heating side

essex boy, April 2014