On Monday, January 9, 2017 at 9:54:42 PM UTC, John Rumm wrote:
On 09/01/2017 20:04, Grumps wrote:
On 09/01/2017 18:49, John Rumm wrote:
On 09/01/2017 16:39, Grumps wrote:
On 09/01/2017 16:25, Clive Arthur wrote:
On 09/01/2017 16:09, Grumps wrote:
On 09/01/2017 15:29, Tim+ wrote:
Grumps wrote:
Happy New Year etc.
Brexit, Daesh, Trump etc, blah blah, but more importantly my
boiler is
having issues.

No hot water this morning and it was evident that the boiler (a 30
year
old Potterton) was off.
It restarted OK and ran for a few minutes.

I changed the thermocouple but it behaves the same.
In fact, if it's just the pilot that is on, then it stays on. It's
only
when the burners start that it shuts down after about 2-3 minutes.

Any ideas or is it time to call a man in?
Ta.


Is the pump running? Does it have an overheat stat that automatically
resets or is it one that you have to manually reset?

Tim

The pump runs (or sounds like it).
The overheat stat automatically resets.

This happened to my dad's boiler. The pump wasn't pumping, as Tim
hints, and the boiler was shutting down on overheat a few minutes after
firing up.

Before it shuts down, feel the pipes either side of the pump. If it's
pumping, they'll be much the same temperature. In my dad's case, there
was a clear difference in temperature, and a replacement pump
(ToolStation IIRC) fixed it.

(The 'heating engineer' dad had called couldn't find the fault. To be
fair, I think that's because he was as thick as ****.)

Cheers

The pump sounds like it's running, and the temperature both sides feels
about the same. The boiler only runs for a few minutes so it doesn't get
very hot.

Last time I saw a similar failure mode, it was a knackered gas valve.
The test would be to stick a volt meter across the mains input on the
gas valve. If its still got 240V present when it shuts down, then the
valve is knackered.

I lit the pilot and fired up the burner. The voltage on the gas valve
was 240V (white and blue wire if there is a standard).
In failure mode, the burner and pilot go out and the voltage on the
valve remains at 240V.

Would that not to be expected though? The CH controller is still asking
for heat, but for whatever reason the boiler has shut off as it thinks
there is no flame.

If there is mains on the valve, then that means the controls are still
calling for heat. Any additional internal stats in the boiler are
normally placed in series with the call for heat to the valve. So if
there is mains on the valve, it suggests all the other interlocks are
closed.

Even after a failure when the pilot and burner are out, when the CH
controller asks for heat the valve gets 240V, and when it's not asking
for heat the valve gets 0V.

Yup that's what you would expect.

The only bit I am not sure off (since I have never tried it) is what
happens if you have mains on the valve, but then the current from the
thermocouple is withdrawn. That would close the pilot part of the valve,
but I don't know what it would do to the main burner. I am guessing it
would have no effect.

That can't be right can it? Surely if the pilot goes out then all gas must be stopped regardless of whether there is 240V or 0V on the valve.



Robert