Firebird C26 problems

[Macperc]

Hi,

Would really appreciate some advice regarding an issue with my Firebird C26 Enviromax.

I woke up the other day to find a strangely hot house (CH turned off) but no hot water. On checking the boiler, the burner was not working but CH pump still running. The burner control box was lifeless despite having a live feed, the boiler pressure was also down to to .5 bar. I replaced the control box and the boiler now runs but will not stop running (burner and ch pump). Pressure increases into the red, limit stat light turns on but still the boiler won’t stop. I checked the expansion vessel, which had water on the air side. I replaced this today but still have the same issue, the the boiler won’t shut down.

Any ideas please?

 

[Macperc]

Does it sound like the high limit stat has failed?

 

[oilhead]

You need to establish where the live feed is coming from to keep your boiler on. If the high limit warning light is on, you should have no power to the control box.

 

[Terrywookfit]

Did you fit the correct control box.
Some have a permanent and switched live to provide a post purge.

 

[Macperc]

Ok thanks, the control box def still has power with the high limit stat light on.

My brother had the exact same boiler, I’ve double checked the control box against his and there’s no difference.

 

[Macperc]

Any suggestions how I track down the source of the live? I have a multimeter although I’m still learning how to use it. Really want to sort this myself but is it time to admit defeat and call in an expert?

 

[Terrywookfit]

Is the control box a MO 535 MPF ?

 

[Macperc]

No, I changed it for a 535 SE LD (non digital). The engineer did the same to my brothers as we were both having repeated problems with the MO version failing (and it’s cheaper).

 

[Terrywookfit]

You will need to alter the wiring.

 

[Macperc]

I compared it to my brothers and the only difference I could see was the heat demand wire was left disconnected so I copied this. I take it I’ve over simplified the job a bit! That doesn’t explain why the original MO535 control box died to begin with though, I presumed this was linked to the boiler not switching off, maybe unrelated. Thanks for the help by the way.

 

[oilboffin]

I thought the mo box was for the wooostteer only firebird have a different box.Bob

 

[Terrywookfit]

I thought the mo box was for the wooostteer only firebird have a different box.Bob

Worstshitter is MO535 MRISF.
FB is MO 535 MPF

 

[Terrywookfit]

I compared it to my brothers and the only difference I could see was the heat demand wire was left disconnected so I copied this. I take it I’ve over simplified the job a bit! That doesn’t explain why the original MO535 control box died to begin with though, I presumed this was linked to the boiler not switching off, maybe unrelated. Thanks for the help by the way.

From memory the heat demand wire is fed by control stat.
The p/L is via limit stat.
If fitting a non digi box the stats need wiring in series with s/l

 

[oilboffin]

Always better to fit the right box less hassle.Bob

 

[Macperc]

I had a really good look at my brothers boiler today and really can’t see any difference in the wiring.

I’m wondering what caused the original MO control box to give up the other day, the boiler lose pressure and the CH pump to continuously run?

I think I’m going to have to buy another MO box to rule this out and then try and work out what the route cause of the original issue is.