Boiler Lock Out

[garrytheskate]

Sometimes when the CH or HW calls for heat the fan comes on and just as the boiler fires it goes to lock-out.
Replaced circuit board, ingnitors, temp sensor and presure diff sensor.
One thing that also happens now and again is that there is a bang as if a valve is sticking. (Have replaced the 3-port but not the CH 2-port valve)
Could it be that if the CH valve is not operating correctly the boiler could go to lock-out
Regards
Apologies
Boiler: Saunier Duval SB30 - 10 years old

 

[45yearsagasman]

I can only guess as you give little useful information about your system.Motorised valves would not cause boiler lockout.

 

[xr4x4]

sounds poss that the bolier is firing but the photo cell doesnt see a flame so cuts the fuel and goes to lock out.

have you checked the photo cell? if its full of soot, there maybe another problem.

 

[bengasman]

sounds poss that the bolier is firing but the photo cell doesnt see a flame s

I must be lagging behind, never seen a boiler with a photocell.

 

[xr4x4]

funny man...

i just assumed it was a oil boiler, as ive never heard the term 'lock out' on a gas boiler.

 

[Boilerman2]

All of this proves the lack of useful info given by the OP

Fuel type = oil / gas / LPG
Boiler Make = abc
Boiler model xyz
Combi /Regular

Info on fault

all of this will result in some useful feed back!

 

[bengasman]

funny man...

i just assumed it was a oil boiler, as ive never heard the term 'lock out' on a gas boiler.

I see. You ass-u-me-d.
I've got news for you. Assumption is the mother of all fuck ups.

 

[Agile]

I must be lagging behind, never seen a boiler with a photocell.

Many oil boilers use a cadmium sulphide photocell to sense the flame by means of the light output. The glass viewing window can get dirty after some use and needs cleaning from time to time.

I can only assume that because the flame does not "sit" on a burner that flame rectification would not be a reliable method. Or alternatively because there can be plenty of soot around that the insulators would become compromised.

Tony

 

[RABAM]

Had two OFTEC engineers to fix our boiler lockout.
First renewed all working parts and told me to lift my oil tank as it still LO'd.
Still a mystery to him why vitiation of flue gases was occurring.

Engineer no. 2 confirmed vitiation of flue gases. Told us the boiler was shot and we needed a new one.

Why had neither of these guys taken the blanking plate off the flue duct to inspect it, like I have just done, to find a hole in the flue pipe?

It has only cost me £600 to find the problem out myself!

What we learn is that if the problem is contamination of the flue then don't forget to inspect the flue.

 

[Agile]

I am very sorry that you had two engineers who failed to identify a simple fault. I am sure that the experienced people who advise on this forum would have found it.

The reality is that a wide spectrum of people take on this work and whilst they can probably manage in 90% of cases in a minority of faults they dont have the backup of more experienced people they can call on to assist so they just tell you that you need a new boiler which is a nice big job for them!

Its not an ideal situation and the only solution is to find a competent engineer and stick with them!

Tony Glazier

 

[dcawkwell]

Air pressure switch?