kiich wrote:

Dave - thanks for the reply.


With the system all switched on - ie heating and hot water - turning down the cylinder stat (you should hear it click) while the room one is higher
than ambient temp should force the motorised valve to the heating position, and you should hear this happening.


ok - here is my steps:

1) set the boiler program to be for both HW and CH
2) boiler comes on
3) turn down the thermostat on the cylinder - i hear that "click"
4) boiler turns OFF

Ah, that sounds to me like the system is not seeing a demand from the
room stat. It may be it is not working correctly, or there is a wiring
fault, or a fault with the programmer, or the programmers settings are
wrong.

Room one - you mean any room in the flat? well all the room are pretty
cold (since no CH is coming on!)

I think he meant "room one" as in *the* room thermostat (as opposed to
the cylinder one)...

after step 4), then thats it for me - nothing else seems to happen.

If it were a fault with the valve, you would expect the boiler to keep
running, but the hot water from the boiler to still get directed to the
HW, rather than being switched to the rads.

why would having room one higher than ambient temp 'force' the
motorised valve to the heating position?

Your room thermostat is a simple device. It either "calls for heat" or
it doesn't. When the room is colder than the setting on the front of the
stat it will call for heat. When the room gets warmer than the setting
on the stat it will stop calling. The idea being that it cycles the
boiler on and off to keep the room temperature at about the setting on
the stat.

wouldnt that happen when the room temp is lower than my room thermostat
settings? i.e. LOWER than ambient temp?

Yes that is what Dave was saying.... just a bit of confusion over room
one ;-)

They're normally wired for hot water priority, so if both stats are
calling for heat, the water one wins.


'They' as in the valve right?

Yup...

If you have a mid position valve, then in response to a demand from
water and heating then it will sit in the mid position - hot water from
the boiler ought to then flow to both rads and cylinder. If it is a
diversion type, then the hot water will probably take priority should
both call at once.

so can i unscrew the screws on the valve and take off the cream plastic
casing to look inside without killing myself?

Without it killing you, yes ;-)

(what you do to yourself is your own business!)

So if the hot water works, this means (please confirm someone)

a) Water pump is working

Yes...

b) Valve is working for hot water

Sort of... if the valve were not working (i.e. failing to switch) it
would still be working for hot water!)

It sounds more like the problem is with demand from the rooms stat though.

What type of stat is it?

Clunky manual:

http://www.screwfix.com/app/sfd/cat/...22657&ts=35413

or something a bit more digital?

Chances are if it is a manual one then you should hear a click as you
rotate the knob from one end of travel to the other. (the click will
occur at around the point of rotation corresponding to the current room
temperature).

Do you have a multimeter?

If not, go buy one (a simple five quid one from Maplin will do).

With the power off, have a peek at the wiring inside the room stat and
report back. We will tell you where to stick the probes to diagnose what
is going on with the stat ;-)

(the plan here is to prove that the room stat is working, and then trace
back through the system til you find the bit which is not)

correct? Should the water pump and the valve making some
noise/vibration when everything is working? its hard to tell from mine
- when boiler comes on, the pump does seem to be vibrating and so does
the valve - but its so little vibration, i'm not sure if it is the
boiler's vibration filtering on to them (since they are so close to
each other) ?

Nothing wrong with that! Pumps are designed to run quietly with as
little vibration as possible - most folks would rather listen to the
telly than have to listen to their central heating.

The valve will only make a sound (if at all) when moving from one
position to the other.

--
Cheers,

John.

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