[John Rumm]

Got summoned by SWMBO to investigate the case of the gas oven not
fulfilling its number one purpose for being...

Symptoms seem to be:

It had preheated and was running ok. Set to gas mark 8 it had been on
for 20 - 30 mins when the igniter started sparking intermittently. The
rate of ignition attempts increased until almost constant. At this point
she turned it off and called me. I relit it, and it went into pre-heat
ok, and appeared to be working normally again[1]. However, shortly after
it resumed the previous behaviour. SWMBO also reported a smell of
unburnt gas which would suggest a genuine flame failure. She found that
if it was turned down to gas mark 6, then it stopped attempting to
ignite, but going back to mark 8 caused a resumption of the problem.

So, likely causes? What to investigate next?

Oven is in a Parkinson Cowan "slot in" cooker. Approx 14 years old.

[1] Although I did not actually test the gas pressure at the time, I did
verify that there was no apparent drop in flame height when the boiler
kicked in for HW production (35kW).


--
Cheers,

John.

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[Ed Sirett]

On Sun, 14 Jan 2007 02:23:36 +0000, John Rumm wrote:

Got summoned by SWMBO to investigate the case of the gas oven not
fulfilling its number one purpose for being...

Symptoms seem to be:

It had preheated and was running ok. Set to gas mark 8 it had been on
for 20 - 30 mins when the igniter started sparking intermittently. The
rate of ignition attempts increased until almost constant. At this point
she turned it off and called me. I relit it, and it went into pre-heat
ok, and appeared to be working normally again[1]. However, shortly after
it resumed the previous behaviour. SWMBO also reported a smell of
unburnt gas which would suggest a genuine flame failure. She found that
if it was turned down to gas mark 6, then it stopped attempting to
ignite, but going back to mark 8 caused a resumption of the problem.

So, likely causes? What to investigate next?

Oven is in a Parkinson Cowan "slot in" cooker. Approx 14 years old.

[1] Although I did not actually test the gas pressure at the time, I did
verify that there was no apparent drop in flame height when the boiler
kicked in for HW production (35kW).


My guess is that the oven has a flame sensing/ignition probe when the
flame goes out the ignition start sparking.

The flame is going out for any number of reasons, when the 'regulo' is
operating the reduced rate is not enough to keep the flames going.

Again I'm guessing but I'd suspect the low rate bleed hole in the valve
has become blocked. Replacement of this valve would be indicated after
checking the burner for dirt and the gas supply pressures.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

[John Rumm]

Ed Sirett wrote:

My guess is that the oven has a flame sensing/ignition probe when the
flame goes out the ignition start sparking.

Yup it does. It appears to be correctly positioned in the flame.

The flame is going out for any number of reasons, when the 'regulo' is
operating the reduced rate is not enough to keep the flames going.

Just seemed odd that it only kicked in at higher heat settings. At mark
6 for example it was ok.

Again I'm guessing but I'd suspect the low rate bleed hole in the valve
has become blocked. Replacement of this valve would be indicated after
checking the burner for dirt and the gas supply pressures.

Thanks Ed.

I got SWMBO to give the burner assembly and surrounding area a good
de-grease, and vacuumed it as well. Since then it seems to be behaving.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/