My Vokera Excell 80 SP boiler will heat the radiators, but it doesn't
seem to know when the taps are switched on, as such the hot water
I have checked the pressure, and it's about 1.5bar.
Can anyone suggest how I might troubleshoot the problem further?
The installer manual for it has good fault finding flows and is available from
http://www.vokera.co.uk/ (needs flash), head for Installer > Product Info >
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:
They are pretty trade oriented so may be less likely to help an amateur but
there is a lot of useful existing content.
Plusnet - I hope you like vanilla
> This boiler gets mentions here quite a lot
I've come to know the 80SP quite well over the last few months...
> 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,
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
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.
> When the arm has reached full travel a microswitch ("domestic
> microswitch") which initiates the firing sequence.
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