Steve Moore wrote:

"Richard J." wrote in message
...
Giff wrote:
Thanks for you help. I've wired it all up and the heating is now
switched by the timer.

The only strange thing I've found is that when I switch the heating
on with the timer, I can hear the boiler fire up and you can see it
light. When I switch it off, the heating switches off but the boiler
is still making a noise. Sounds like a fan but the fan isn't on. If I
switch the heating off using the switch on the boiler then the noise
goes likewise if I turn the hot tap on and then switch it off, the
noise goes.

Our combi (not a Vaillant) does this too, and the noise is from the
central
heating pump. Even if we switch the CH off, the pump keeps on running.
Using a hot tap will always shut off the CH and the pump on our system,
and
this is why the noise stops if we turn a hot tap on for a second or so.
Maybe your system has the same logic.
--
Richard J.
(to e-mail me, swap uk and yon in address)

moved from top post
Known as overrun & takes away residual heat from the core while the burners
and body cool down.

Steve


The length of time this happens for is adjustable. See the installation
and servicing guide.

ON Turbomax+ models (leds + digital temp display) its done by changing a
setup number in the control computer.
On plain Turbomaxs (ladder of Leds) the manual simply says it is
automatic (and gives no indication whether it is adjustable or not).

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html