Vokera Linea Plus combi, fires up, CH gets up to mid-70s temp if set to
max (never to the 78/82 which I seem to remember being its max). The
pump seems to be working. Flow pipe gets hot. The boiler then
modulates down briefly after hitting 74/75 and then shuts off pretty
much straight away. Waits 3 minutes aby which temp reading is down in
the 30s/40s, fires (after the 3 min lock times out), gets back up to
70s, modulates down and shuts off again. Repeat ad infinitum. Result
cold house. Add cold grumpy wife into the equation. Help!

"Bolted" wrote in message
...
Vokera Linea Plus combi, fires up, CH gets up to mid-70s temp if set to
max (never to the 78/82 which I seem to remember being its max). The pump
seems to be working. Flow pipe gets hot. The boiler then modulates down
briefly after hitting 74/75 and then shuts off pretty much straight away.
Waits 3 minutes aby which temp reading is down in the 30s/40s, fires
(after the 3 min lock times out), gets back up to 70s, modulates down and
shuts off again. Repeat ad infinitum. Result cold house. Add cold
grumpy wife into the equation. Help!



Is this pump really working properly? I had a similar problem on my (Eco
Hometec branded) MAN Micromat a while ago where it kept cutting out with a
"flow/return limit" error message. The pump appeared to be running but on my
boiler it is a fully variable modulating pump. It was only running at about
its slowest speed and never going up to full speed to circulate that
super-hot water out of the boiler. Result was the flow temperature shooting
up very quickly, followed by the burner (also infinitely variable)
modulating down, and the flow temperature exceeding the limit fairly quickly
causing a shutdown.

The 240V supply to my pump is turned on or off by a relay on the controller
board, but the speed is varied by a PWM signal on a third wire. I could see
the PWM signal varying but the pump was staying at around its slowest speed.
Fortunately they still supply these and it has been running fine since it
was replaced.

On my boiler in the setup menu you can adjust the max pump speed. While
adjusting it it rather handily keeps the pump running and you can check
whether the pump is actually responding to the variable speed signal. Maybe
your boiler has a similar feature?

HTH.

Regards,
Simon.

On 10/11/2010 23:41, Simon Stroud wrote:
wrote in message
...
Vokera Linea Plus combi, fires up, CH gets up to mid-70s temp if set to
max (never to the 78/82 which I seem to remember being its max). The pump
seems to be working. Flow pipe gets hot. The boiler then modulates down
briefly after hitting 74/75 and then shuts off pretty much straight away.
Waits 3 minutes aby which temp reading is down in the 30s/40s, fires
(after the 3 min lock times out), gets back up to 70s, modulates down and
shuts off again. Repeat ad infinitum. Result cold house. Add cold
grumpy wife into the equation. Help!



Is this pump really working properly?

Thanks for the response.

It's one of my main suspects - I took it off and it looked fine, and ran
fine, and quietly. I didn't test its torque at all, maybe I should
have. It makes a bit of a clicky rattly racket when installed though,
and there isn't a great deal of sign of flow noise in the rad tails
(latest test inspired by your post).

Hmm.

Nothing so fancy as your boiler, so it's either broken or not.

Another oddity I found by accident is that the boiler (water) pressure
switch seems to have gone. It was happy to try and run with 0 bar in
the system. I'll replace it obviously, but I'm struggling to see how
that would cause the CH-only problems.