idle curiosity

[breezer]

just wondered, in general on a gas boiler, (electronic ignition) to light the gas does the spark run for a preset time, or is there a "sensor" that says "gas lit stop igniting"

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oil boiler

does it have a pilot light or are they too electronic ignition, and if so same as above.

as i said i am only wondering in general

 

[oilman]

OIL BOILER

Pressure jet types have spark ignition started after a purge period, and runs for a set time.

Vapourising types have a glow plug which is heated for a set time, or might be manually controlled.

 

[breezer]

Thanks oilman , as i said it was just idle curiosity, but now i know

 

[soubriquet]

Gas boiler runs fan first, checks for positive pressure, enables spark, enables gas. If the flame lights, the clever bit starts... the flame conducts electricity, and has the interesting quirk of converting ac current to dc. (flame rectification, it's called). The control box is looking for the dc return, and if it finds it, it knows there is a flame, and can halt the spark. There is usually a time allotted after which if no flame is sensed, the gas is disabled, then the spark, then the fan. A warning light shows there is a problem and the boiler is said to have 'locked out'. Some larger boilers sense the flame by its ultra violet emission, but otherwise the system is similar.

 

[IanDB]

You live and learn. I've never even heard of flame rectification. Whoever thought of that one? And for all these years I though it was detected by a thermocouple.

 

[breezer]

Gas boiler runs fan first, checks for positive pressure, enables spark, enables gas. If the flame lights, the clever bit starts... the flame conducts electricity, and has the interesting quirk of converting ac current to dc. (flame rectification, it's called). The control box is looking for the dc return, and if it finds it, it knows there is a flame, and can halt the spark. There is usually a time allotted after which if no flame is sensed, the gas is disabled, then the spark, then the fan. A warning light shows there is a problem and the boiler is said to have 'locked out'. Some larger boilers sense the flame by its ultra violet emission, but otherwise the system is similar.

now thats what i call clever

 

[oilman]

I found this . Makes me think flame rectification might not be used on domestic boilers.

 

[AlanE]

All modern gas boilers use flame rectification. Thermocouples went out with the demise of the permanant pilot.

Those modern boilers using pilots only do so as an inbetewwn measure. Spark lights pilot which in turn lights main boiler. When the demand for the boiler ceases so the pilot extinguishes.

The use of permanant pilots would greatly reduce thge SEDBUK rating for the boiler as it would be burning gas continually.

Alan

 

[soubriquet]

Thanks, Oilman, for that link, I'm a potter as well as a plumber, so info on kiln burners is always of interest.
Any modern domestic boiler is likely to use flame rectification. There are two spark electrodes often at opposite ends of the burner bar. If you listen as the burner lights, you@ll hear the buzz of the spark go silent.
the spark generator keeps going. if you simulate a flame fault by turning the boiler gas supply valve off, as you see the flame die and become intermittent, you will see the sparks return. If the boiler does not sense rectification after a set period it will go to lockout, and a light will come on to tell you to call for a service engineer, as we are now increasingly called.

And by the way, the recent British Gas adverts are a joke in more ways than one..... I wouldn't want someone stupid enough to put up with that to go anywhere near a gas pipe!

 

[AlanE]

When mentioning british gas it should be remembered that they do NOT carry out routine servicing on gas appliances covered by their 3* service.

They carry out an annual performance and safety check - they check flue gas and then decide whether to even take cover off of the boiler.

NOT the requirements as laid down by the manufacturers.

Alan

 

[ollski]

Dpends on the general condition of the boiler and obviously the type Alan. An open flued appliance will always get a full service at the annual inspection. A negative pressure room sealed boiler may just get a performance and safety check if that is all that is required, after all people on a 3 star contract want a safe appliance and quick repairs with no huge bills and that is what they get.