In an earlier contribution to this discussion,
keith wrote:

Please can someone help me tell if our CH is faulty or if i've just
got the settings wrong?
There are more knobs to fiddle with on than the CH in our previous
house & I'm not sure what thay do or how they interact.
Pictures at :

www.dulwich.net/ch

CH works OK during day on timer, but seems to "go to sleep" at night
(even when timer says ON and thermostat is calling) and won't get
radiators warm. Also doesnt start warm in the morning. Plenty hot
during day!

I've managed to "wake it up" last 2 nights by 1-Switching programmer
on & off at mains or 2- turning up the knob on the water tank.

I can work the thermostat and timer (just like old house) but this
one also has a big knob 0-5 on the gas heater (see pictures) which
makes the gas flame appear & go higher sometimes, other times turning
it up has no
effect - no flame to be seen.

What is this knob supposed to do & what should I be doing with it &
how does it interact with the knob on the water tank, which I think
is the water temperature?
(see pictures)

Have I got one of these knobs too high or something to cause the
problem?

Thanks

It sounds from what you say that the radiators only get hot when there is
*also* a demand for domestic hot water. Has it ever worked properly? If not,
it has not been installed and/or wired correctly. From your photos, you have
a Y-Plan system - fully pumped, with a mid-position 3-port valve to direct
the water to the cylinder and/or radiators. [See
http://content.honeywell.com/uk/homes/systems.htm and scroll down to Y-Plan]

This system requires the programmer to have a "HW Off" terminal in addition
to "HW On" and "CH On" and it also requires the cylinder stat to have
change-over contacts. If this is not done, the system won't work in CH-only
mode.

If it *has* worked but has since stopped working, my money would be on a
duff microswitch in the actuator on the 3-port valve. In the CH-only
position (with HW turned off or satisfied) the system relies on this
microswitch to turn the boiler and pump on.

Incidentally, the knob on the boiler only controls the temperature of the
water produced by the boiler - unless you turn it right off - not whether it
operates or not. Your problem is either in the wiring or in the actuator.
--
Cheers,
Set Square
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