In an earlier contribution to this discussion,
bachippy wrote:

Please could someone advise me on the following situation.

My system comprises Suprima 50 boiler (recently thoroughly checked by
portterton engineer when replacing parts), Honeywell 4073 3 port
valve, Honeywell room stat, Potterton EP3002 programmer, Honeywell
cylinder stat, Grundfos pump and Honeywell frost stat.

The 3 way valve, room stat and programmer were new with the boiler
parts and have been wired in by a qualified electrician according to
the wiring diagrams using a Honeywell 10 way junction box, he has used
new wiring for all the components thus rewiring the whole system as
per the diagrams.

The electrician has spent 3 whole days checking and rechecking the
wiring, looking at boiler wiring diagrams as well as the Sundial Y
diagrams and the valves and programmers own ones. He is now at a total
loss and I am just in despair.

The problems encountered include:-

Phantom boiler running, as if frost stat telling boiler it's too cold
- hopefully now resolved, should know later, hopefully the boiler
won't come on of it's own accord.

Radiators getting hot when only hot water is on - still unsolved. When
hot water on the manual lever is in the auto position with resistance
to being moved. When the CH is switched on the lever becomes loose
with no resistance. When the CH is switched off the motor whirrs and
the resistance returns.

Tonight when the programmer got to the set time to come on the boiler
lights showed that it was not getting instructions, however when the
room thermostat was turned right up to over 25C the boiler fired.
However when the programmer switched off the boiler kept going until
the room stat was turned down.
Clearly this is no good if I want the programmer to come on to heat
water early in the morning, when I'm asleep, as I'd have to be up to
adjust the room stat to make the boiler light.

He's convinced it must be a problem somewhere in the wiring but says
he has run out of options and doesn't see how it can be wrong when it
is exactly as the diagrams show.

Please help.

Assuming that the kit is all working properly, there must be *something*
wrong with the wiring!

I'm not aware that the Honeywell Y-Plan wiring diagram makes any provision
for a frost stat. Exactly where is this connected? My hunch is that the
problem is in this area.

The other possibility is that some of the connections are reversed on the
cylinder stat. Bear in mind that HW OFF is live when HW is off at the
programmer. If this is wrongly connected at the cyl stat, such that it's
getting connected to the boiler when it shouldn't be, strange things are
likely to happen.

If your man has been staring at it for 3 days, he's not going to find the
deliberate mistake now. You need a fresh pair of eyes to look at it.
--
Cheers,
Roger
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