On Wed, 8 Mar 2017 03:04:58 -0800 (PST)
RobertL wrote:

On Wednesday, March 8, 2017 at 10:45:47 AM UTC, Michael Chare wrote:
On 08/03/2017 10:07, Bill wrote:
For once this is my problem rather than sons or daughter.

Our central heating appears to be a basic S-type system with a
Vaillent Ecotec Plus 428 boiler, Siemens RWB2E timeswitch and
RCR10 wireless room stat. 2 Zone valves, one for CH, one or hot
water. All installed by a local company about 10 years ago.

Because of my persistent bad back, I don't feel safe climbing
into the airing cupboard and measuring voltages after taking
covers off the boxes there.
I have reset and checked the 2 controllers and all lights come on
as expected as dials are turned.

For about 5 days now the heating has been staying on all night.
I've been looking at the diywiki site and can't see how, with the
stat and timeswitch set to OFF, the system can be running. I
can't believe that both timeswitch and stat could have both
failed at the same time.

Is there something I'm missing?

Stuck Zone valve?


--
Michael Chare

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On my CH zone valves you can feel with a finger underneath and find
the spring-loaded lever that should be moving the valve. You can
feel this change from being 'loose, to 'tight' when the valve
opens/closes without needing to take the cover off.

The firing of the boiler is usually determined by the actual position
of the physical valves, rather than what their commanded position
is. So if they get stuck open then the boiler fires.

That is exactly the fault that my system had. Even with the Programmer
set to 'Off' for both CH and DHW, the boiler was still getting a 'Run'
instruction. Removing the zone valve actuator and working the valve
stem fixed it.

--
Davey.