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[Field Marshal Dr. Opti]

20 year old HRM Wallstar boiler that runs on oil.

It turns over for about 15 seconds before lock out and then a red light. Try again (repeatedly) and the same thing happens. No ignition.

Plenty of oil in the tank, and you can see it being drawn up the pipe to the pump.

It was working OK a few days ago.

I'm wondering if it is the photo cell as I think it may be the original but could be completely wrong.

Anyone boiler savvy on here?

[Sir Tigger KC]

Have you tried asking your favourite AI bot?  ChatGPT? Grok? etc 

I believe they're quite clever these days. 

[STEMO]

Have you tried asking your favourite AI bot?  ChatGPT? Grok? etc 

I believe they're quite clever these days. 

I asked 


This sounds like a classic ignition failure issue with your oil-fired boiler. The 15-second run before lockout is typical for the safety time-out period, where the control box tries to establish a flame. Since it fails to detect a flame, it shuts down to prevent unburnt oil from accumulating, which is a significant hazard.
Given the age of the boiler and the symptoms, here are the most likely causes, ranging from simple to more complex:
🔍 Most Likely Causes of No Ignition
1. Faulty or Fouled Electrodes
The ignition electrodes are responsible for creating the spark that lights the oil spray.
• Symptom: No spark at all, or a weak/intermittent spark.
• Cause: The porcelain insulators can crack, or the electrode tips can become dirty, covered in soot, or incorrectly positioned due to wear. This prevents the high-voltage electricity from creating a strong, consistent spark.
2. Failed Photocell (Cad Cell)
The photocell or Cadmium Sulphide (CdS) cell is the "eye" of the boiler. It detects whether a flame is present.
• Symptom: The burner might spark and even ignite for a second, but the photocell fails to sense the flame, or it's simply failed. Since the control box doesn't register a flame within the 15-second window, it locks out.
• Cause: The cell itself has failed, or more commonly, it's covered in soot and can't "see" the flame even if it ignites. The photocell is a common point of failure for an older boiler.
3. Oil Nozzle Clog or Failure
The nozzle atomizes the oil into a fine mist so it can be easily ignited by the spark.
• Symptom: The burner motor runs, the pump is drawing oil, but the spray pattern is poor or non-existent, preventing a proper flame.
• Cause: The tiny orifice of the nozzle can become clogged with sludge or debris from the oil line, especially after the boiler has been sitting or the fuel filter is due for a change. Given the boiler's age, a worn nozzle is also highly probable. Nozzles should be replaced annually.
4. Air-Lock in the Oil Line
Although you see oil being drawn, there might be a small air bubble (air-lock) trapped in the pump or oil line, particularly if the oil level dropped very low recently or if the system has been opened.
• Symptom: Oil is supplied, but the pump cannot maintain the pressure needed to atomize the fuel properly.
• Fix: An engineer would bleed the pump to remove the air.
5. Failed Oil Burner Control Box
The control box (often a small black or grey box on the burner) manages the entire sequence: pre-purge, spark timing, fuel solenoid, and monitoring the photocell.
• Symptom: The cycle fails, even when all other components are working.
• Cause: Internal electrical failure. This component often requires full replacement.

[Sir Tigger KC]

I think our Lord should get rid of that dirty old boiler, replace it with an Air Source Heat Pump and save the planet! 

[Field Marshal Dr. Opti]

Have you tried asking your favourite AI bot?  ChatGPT? Grok? etc 

I believe they're quite clever these days. 

I asked 


This sounds like a classic ignition failure issue with your oil-fired boiler. The 15-second run before lockout is typical for the safety time-out period, where the control box tries to establish a flame. Since it fails to detect a flame, it shuts down to prevent unburnt oil from accumulating, which is a significant hazard.
Given the age of the boiler and the symptoms, here are the most likely causes, ranging from simple to more complex:
🔍 Most Likely Causes of No Ignition
1. Faulty or Fouled Electrodes
The ignition electrodes are responsible for creating the spark that lights the oil spray.
• Symptom: No spark at all, or a weak/intermittent spark.
• Cause: The porcelain insulators can crack, or the electrode tips can become dirty, covered in soot, or incorrectly positioned due to wear. This prevents the high-voltage electricity from creating a strong, consistent spark.
2. Failed Photocell (Cad Cell)
The photocell or Cadmium Sulphide (CdS) cell is the "eye" of the boiler. It detects whether a flame is present.
• Symptom: The burner might spark and even ignite for a second, but the photocell fails to sense the flame, or it's simply failed. Since the control box doesn't register a flame within the 15-second window, it locks out.
• Cause: The cell itself has failed, or more commonly, it's covered in soot and can't "see" the flame even if it ignites. The photocell is a common point of failure for an older boiler.
3. Oil Nozzle Clog or Failure
The nozzle atomizes the oil into a fine mist so it can be easily ignited by the spark.
• Symptom: The burner motor runs, the pump is drawing oil, but the spray pattern is poor or non-existent, preventing a proper flame.
• Cause: The tiny orifice of the nozzle can become clogged with sludge or debris from the oil line, especially after the boiler has been sitting or the fuel filter is due for a change. Given the boiler's age, a worn nozzle is also highly probable. Nozzles should be replaced annually.
4. Air-Lock in the Oil Line
Although you see oil being drawn, there might be a small air bubble (air-lock) trapped in the pump or oil line, particularly if the oil level dropped very low recently or if the system has been opened.
• Symptom: Oil is supplied, but the pump cannot maintain the pressure needed to atomize the fuel properly.
• Fix: An engineer would bleed the pump to remove the air.
5. Failed Oil Burner Control Box
The control box (often a small black or grey box on the burner) manages the entire sequence: pre-purge, spark timing, fuel solenoid, and monitoring the photocell.
• Symptom: The cycle fails, even when all other components are working.
• Cause: Internal electrical failure. This component often requires full replacement.

I'm thinking this. You occasionally need to clean with a drop of white spirit so it can 'see clearly'

I've done this but still no go.

I could buy a new one but the whole thing is so old and creaky it may not be worth my trouble.

Can you still buy new oil boilers or have the environmentalists put a stop to this?

[Field Marshal Dr. Opti]

I think our Lord should get rid of that dirty old boiler, replace it with an Air Source Heat Pump and save the planet! 

Not while I still have breath in my body.....

They don't seem to work very well from what I hear.

[Field Marshal Dr. Opti]

Fortunately we have a large open fire to fall back on and more than enough free wood available.

Yo can't beat an open fire.

[STEMO]

I think our Lord should get rid of that dirty old boiler, replace it with an Air Source Heat Pump and save the planet! 

Not while I still have breath in my body..... I will never buy an EV that runs on PP9s>

They don't seem to work very well from what I hear.

 

[Field Marshal Dr. Opti]

I think our Lord should get rid of that dirty old boiler, replace it with an Air Source Heat Pump and save the planet! 

Not while I still have breath in my body..... I will never buy an EV that runs on PP9s>

They don't seem to work very well from what I hear.

 

I'd be saving the world twice. Once with a heat pump and again with a milk float.

Even I have my limits.

[Lizzie Zoom]

I think our Lord should get rid of that dirty old boiler, replace it with an Air Source Heat Pump and save the planet! 

Not while I still have breath in my body.....

They don't seem to work very well from what I hear.

I think you may be right Opti.

One of my friends very recently moved into a brand new house which has been fitted with one of these new fangled heat pumps.  Over the last week it has become very cold down here, but she tells me the heating will only get to a certain level and no more, with her bedrooms remaining quite cold!   Another friend of mine is a master builder, and is very well qualified in the plumbing, and electrical, fields.  He says that the heat pumps have a limit on how much heat they actually push out, which is no where near as high as it is with an gas central heating system.

What the hell is going on I think?!!  Why are heat pumps being so enthusiastically promoted if they have limits for houses in our climate?!

[ronnyd]

I think our Lord should get rid of that dirty old boiler, replace it with an Air Source Heat Pump and save the planet! 

With his vast tract of land in rural Lincolnshire, i would think that a ground source heat pump would be more fitting. 

[Field Marshal Dr. Opti]

I think our Lord should get rid of that dirty old boiler, replace it with an Air Source Heat Pump and save the planet! 

Not while I still have breath in my body.....

They don't seem to work very well from what I hear.

I think you may be right Opti.

One of my friends very recently moved into a brand new house which has been fitted with one of these new fangled heat pumps.  Over the last week it has become very cold down here, but she tells me the heating will only get to a certain level and no more, with her bedrooms remaining quite cold!   Another friend of mine is a master builder, and is very well qualified in the plumbing, and electrical, fields.  He says that the heat pumps have a limit on how much heat they actually push out, which is no where near as high as it is with an gas central heating system.

What the hell is going on I think?!!  Why are heat pumps being so enthusiastically promoted if they have limits for houses in our climate?!

Yep...that sounds about right, Lizzie.

I hear they work 'reasonably well' for a few people but poorly for many others.

I'll avoid if at all possible.

[Kevin Wood]

If it's not igniting at all it's not the photocell. More likely the ht transformer, fuel solenoid or pump.

[Sir Tigger KC]

I think our Lord should get rid of that dirty old boiler, replace it with an Air Source Heat Pump and save the planet! 

Not while I still have breath in my body.....

They don't seem to work very well from what I hear.

Until Mrs Opti decides that you need to save the planet a bit more.   

Then you'll be here telling us how fantastic it is, we really don't need to heat our houses to 20 degrees and you didn't realise that 14 degrees can be quite comfortable when you're wearing half a dozen jumpers!