On Wednesday, 8 March 2017 11:20:12 UTC, Bob Minchin wrote:
Bob Minchin wrote:
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?
Is there a frost protection stat that is telling lies? This would
normally be wired to bypass both timer and room stat.
Also check if the "demand" terminal on the boiler is live. If it is not
live and yet the boiler runs, then suspect the control board.
If the demand terminal is live then it is the external controls giving
wrong instructions to the boiler.

the only sure way is to measure voltages to locate the problem. You might be able to pin it down by seeing the result of operating the various controls, maybe.


NT