We have a small gas hob on our boat running from bottled propane.

It has the (mandatory on boats) flame detection failure shut off. Thus
to light the gas you turn the knob, press it in to override the flame
detector, light the flame and keep the knob pressed in for a few
seconds until the flame detector thermocouple (?) has heated up to
keep the gas on.

One of the three burners won't start at all, i.e. pressing the knob to
override the flame detector doesn't allow gas through to the burner.

Does anyone know the likely cause? I.e. is it simply something
sticking in the mechanism which might be fixed by a thorough clean or
is there a specific part which may need replacing?

--
Chris Green
·

Chris Green wrote:
We have a small gas hob on our boat running from bottled propane.

It has the (mandatory on boats) flame detection failure shut off. Thus
to light the gas you turn the knob, press it in to override the flame
detector, light the flame and keep the knob pressed in for a few
seconds until the flame detector thermocouple (?) has heated up to
keep the gas on.

One of the three burners won't start at all, i.e. pressing the knob to
override the flame detector doesn't allow gas through to the burner.

Does anyone know the likely cause? I.e. is it simply something
sticking in the mechanism which might be fixed by a thorough clean or
is there a specific part which may need replacing?

Failing to hold in after lighting is usually thermocouple failure.
Failing to ignite in the first place sounds like a mechanical issue in
the gas valve. I'm assuming it is not a failure of the igniter and you
have tried a match etc and know there is no gas getting through.

Bob

Chris Green brought next idea :
One of the three burners won't start at all, i.e. pressing the knob to
override the flame detector doesn't allow gas through to the burner.

Does anyone know the likely cause? I.e. is it simply something
sticking in the mechanism which might be fixed by a thorough clean or
is there a specific part which may need replacing?

If there is definately no hiss from the gas to be heard, when the
button is pressed, likely the jet is blocked up perhaps with grease.
Usually if the burner is removed, you will see the brass jet which can
be unscrewed. It should have a tiny hole in the end. If you cannot blow
through it, it is choked up. You will need a really fine wire to clear
it.

I had trouble with our caravan's grill, not getting hot. On stripping
it down I found its jet had been drilled too small. I was able to drill
it out to the correct size and it has been fine since. Possibly if your
ring has never worked, this might be the problem. I was lucky, I
already had in my workshop a set of the fine drill bits needed, but
your best option might be a replacement jet, if this is the case.

On Mon, 17 Oct 2016 14:13:51 +0100, Bob Minchin
wrote:

Failing to ignite in the first place sounds like a mechanical issue in
the gas valve.

.... or a jet blocked with crud?



Thomas Prufer

Thomas Prufer wrote:
On Mon, 17 Oct 2016 14:13:51 +0100, Bob Minchin
wrote:

Failing to ignite in the first place sounds like a mechanical issue in
the gas valve.

... or a jet blocked with crud?



Thomas Prufer

Yes but I had rather hoped the OP would have either checked that or seen
gradual degradation in heat output as the jet diameter reduced.

Bob Minchin wrote:
Chris Green wrote:
We have a small gas hob on our boat running from bottled propane.

It has the (mandatory on boats) flame detection failure shut off. Thus
to light the gas you turn the knob, press it in to override the flame
detector, light the flame and keep the knob pressed in for a few
seconds until the flame detector thermocouple (?) has heated up to
keep the gas on.

One of the three burners won't start at all, i.e. pressing the knob to
override the flame detector doesn't allow gas through to the burner.

Does anyone know the likely cause? I.e. is it simply something
sticking in the mechanism which might be fixed by a thorough clean or
is there a specific part which may need replacing?

Failing to hold in after lighting is usually thermocouple failure.

Yes, this isn't the issue.


Failing to ignite in the first place sounds like a mechanical issue in
the gas valve. I'm assuming it is not a failure of the igniter and you
have tried a match etc and know there is no gas getting through.

It's manually lit anyway, so we always use a lighter or a match.
There's no gas getting through.

--
Chris Green
·

Thomas Prufer wrote:
On Mon, 17 Oct 2016 14:13:51 +0100, Bob Minchin
wrote:

Failing to ignite in the first place sounds like a mechanical issue in
the gas valve.

... or a jet blocked with crud?

Hey, that's a point, I have to admit I haven't checked for that very
obvious cause. Thanks Thomas!

--
Chris Green
·

Bob Minchin wrote:
Thomas Prufer wrote:
On Mon, 17 Oct 2016 14:13:51 +0100, Bob Minchin
wrote:

Failing to ignite in the first place sounds like a mechanical issue in
the gas valve.

... or a jet blocked with crud?



Thomas Prufer

Yes but I had rather hoped the OP would have either checked that or seen
gradual degradation in heat output as the jet diameter reduced.

No, the OP hadn't thought of the obvious! :-)

While we would have noticed a slow deterioration it might well have
got some dirt stuffed into it during fairly major works recently. I
only tried to use the gas again after it not being in use (and the gas
completely disconnected) for some weeks.

--
Chris Green
·

On Tue, 18 Oct 2016 10:20:14 +0100, Chris Green wrote:

It's manually lit anyway, so we always use a lighter or a match.
There's no gas getting through.

If it's not the jet, the thermocouple is (almost?) always replaceable, often by
a generic part. And AFAIK the electromagnet that the thermocouple feeds is also
replaceable, sometimes.


Thomas Prufer