Vokera Excell 80 SP - No Hot Water

In article , snipped-for-privacy@gmail.com writes

This boiler gets mentions here quite a lot so you could do worse than doing a google groups search for it.

The installer manual for it has good fault finding flows and is available from

Discontinued Products. Reading this will let you know what bits are where and guide you through a fault finding session.

The flow switch would be a prime candidate and easy to check, disconnect power, turn on tap and check for operation of the switch using a multimeter on ohms/continuity. Next best is probably the diverter valve, check back at previous posts as this is mentioned there. Finally, the soldered joints on the pcb for the H/W (and C/H) temp control are prone to failure, an easy job to re-make them if you can solder but leave that option til last (if wiggling the spindle causes a momentary spring back into life then this is a good bet).

This is a pretty simple boiler so is a good candidate diy but watch out for live parts and don't touch gas carrying parts unless you are competent.

Oh, also see the Gas-News forums:

Good luck.

I've come to know the 80SP quite well over the last few months...

In this design secondary water flow is sensed hydraulically by pressure difference across a diaphragm (the "domestic diaphragm") which moves a push-pin which operates a pivoted arm (the fulcrum arm) which in turn operates the diverter valve mechanically. When the arm has reached full travel a microswitch ("domestic microswitch") which initiates the firing sequence.

Firstly check that the arm is moving full-travel when secondary water is flowing - full-travel being far enough to operate the microswitch. If not, I'll lay a penny to a pound that the problem is a knackered domestic diaphragm (Vokera part no. 6882, GC no. 301-180). Replacement is an easy job.

If the arm moves OK and the boiler isn't firing I'd look at the domestic microswitch next - this is easily isolated and can be safely tested with a multimeter with the boiler powered down, since operation of the arm does not depend on a supply of electricity.

I'm sorry, I'll write that again:

When the arm has reached full travel it also operates a microswitch (the "domestic microswitch") which initiates [etc.]

Thanks for the details Andy, the one I look after has just developed the same fault, H/W only when C/H is already on, I'll make sure I have the diaphragm when I get round to looking at it.

You get those symptoms when the diaphragm starts to fail; the arm moves enough to give partial operation of the diverter valve, but not enough to activate the DHW microswitch. IME it deteriorates rapidly after that and you'll soon have no HW at all, even if the burner is already firing for CH.