Have a look on rielloburners.co.uk they have fault finding flow charts on there.
Worcester Heatslave oil boiler - lockout after draining and refilling system. Can't figure out why.
- Thread starter bigbob764
- Start date
Once you have ensured that the burner is free, and that the oil pump is not stiff, consult the Riello guide, and also google Worcester oil burner hard reset.
Personally I think it is time to consult an experienced technician.
Personally I think it is time to consult an experienced technician.
Update: bought a replacement control box and fitted it. Boiler fired up first time. Seems to be running OK now.
The old control box presumably failed in some way, although visually it looks pristine. I assume something on the PCB got fried when the capacitor leaked. I probably didn't need to replace the fan motor, but will keep the old one as a spare.
Thank you to everyone on here for their input.
I will shortly leave a comment with a brief "tutorial" for people who might need to do the same in future.
The old control box presumably failed in some way, although visually it looks pristine. I assume something on the PCB got fried when the capacitor leaked. I probably didn't need to replace the fan motor, but will keep the old one as a spare.
Thank you to everyone on here for their input.
I will shortly leave a comment with a brief "tutorial" for people who might need to do the same in future.
You probably know more about oil boilers than me... I rarely see them.
So here is a tutorial on how to diagnose and replace parts on a Riello RDB type burner. I am not an expert but hopefully the following can prove useful to others in the future.
WARNING: Do not attempt any of this unless you are suitably competent. This is not intended as professional advice and is for educational use only. Oil-fuelled appliances can be very dangerous. Make sure you completely understand all the procedures you undertake. Pay particular attention to safety, esp. in relation to electrics, flammable liquids/vapours, and handling of harmful exhaust gases. If you're at all unsure, call a qualified engineer.
You'll need a long 4mm hex key, a Philips screwdriver, a 12mm socket, a spanner, and some pliers.
1. Fault Diagnosis
So your boiler has a burner lockout fault. In my case it was 9F 855. Others have 8F 855 or similar. Most tutorials indicate that this is a fault with the oil feed and advise bleeding air out the oil line or replacing the pump. However you might have a different burner-related fault.
Take a look at the front of the Riello RDB burner. The central reset button doubles as an LED which can flash fault codes. These flashes can tell you what type of error the burner is experiencing. In my case, it was flashing red and orange which indicated a fan motor error.
You can look up the fault code patterns in:
- Your boiler's installation manual [1]
- The Riello manual for your specific burner [2]
- A Riello fault finding diagram for your burner [3]
The manuals also suggest tests you can perform with a multimeter, e.g. ensuring the correct resistance across the motor wires or the capacitor etc. (however in my case these were all correct despite the control box being faulty).
2. Burner Removal
Removing the burner from inside the boiler is something I was unable to find in any videos online. It seemed daunting but is actually very simple.
First, before you do anything, electrically isolate the boiler. Close the kerosene/oil line. In my case, a ball valve was present on the oil feed behind the flexible hose.
Next, ensure your oil line has enough slack in it to allow the burner to be pulled out. If not, you may have to disconnect the hose after isolating the oil supply.
Remove the air intake tube by loosening the jubilee clip and pulling it up.
The burner is held in place by a single hex bolt. Undo this and carefully slide the burner out.
3. Burner Disassembly
There are several helpful videos online showing disassembly of the burner [4][5].
To remove the pump, start by removing the thumb screw and the solenoid (not shown in photo) from the brass piece atop the pump:
Next you'll need to remove the high-pressure copper oil line from the left side of the pump. This line delivers oil from the pump head into the combustion nozzle. It is not the same as the main oil inlet line (the flexi hose), which can be left attached to the pump at all times.
The pump is mounted to the fan motor via 3 x 4mm hex bolts. Undo those and pull the pump out (pump already removed in photo):
Make sure you don't lose the plastic insert which sits on the shaft of the pump.
Next, remove the motor capacitor. (Not pictured.)
Pull off the black plastic cap, and carefully remove the two spade terminals. If you can, discharge the capacitor by bridging the two terminals with the metal tip of an insulated screwdriver. Then unscrew the capacitor from its mounting point.
Note: the capacitor is non-polarised i.e. it doesn't matter which side of the capacitor each wire goes in.
Next, undo the two black fan casings to the right of the burner. These are also 4mm hex bolts.
This will expose the fan's impeller.
Important: Note the ~1mm gap behind the impeller: this gap is important when re-assembling it. The impeller should not touch the body of the burner as this would cause noise, grinding, or siezing of the fan as it spins.
To remove it, undo the 4mm hex grub screw then pull the whole thing off. Mine was very stubborn. I had to spray a small amount of silicone lubricant on the coupling and wrestle it off. (Alternatively, if your fan motor is already broken, you could undo its screws at the front and gently hammer on the shaft to knock the impeller free.)
After removing the impeller, undo the motor's bolts from the other side of the burner, and pull the motor free. You may need to remove the control box to free the motor wires.
Important: Note the thin rubber seal around the mounting face of the motor. Ensure you keep it there when re-mounting the motor.
4. Control Box
Removing the control box is straightforward so I won't detail it heavily. Basically, undo the two bolts holding the box in place. Remove all the terminal connectors from inside the box and lift it away.
There is a square seal, behind which are the wires for the high-voltage ignition electrodes. These are simply pulled away firmly with a pair of pliers. They look like they're held in by small Philips screws, but are not. When reattaching the control box make sure to re-establish the seal and don't pinch any wires.
5. Reassembly
Follow the above steps in reverse order. Make sure the control box wires are inserted firmly and correctly and that nothing is trapped. Make sure all seals are good, and ensure a 1mm gap behind the fan impeller.
Helpful Resources
[1] Worcester Bosch installation manual:
www.worcester-bosch.co.uk
[2] Riello RDB Heatslave burner manual:
[3] Riello RDB burner fault finding chart:
studylib.net
[4] Riello RDB burner assembly:
[5] Riello RDB burner strip down:
WARNING: Do not attempt any of this unless you are suitably competent. This is not intended as professional advice and is for educational use only. Oil-fuelled appliances can be very dangerous. Make sure you completely understand all the procedures you undertake. Pay particular attention to safety, esp. in relation to electrics, flammable liquids/vapours, and handling of harmful exhaust gases. If you're at all unsure, call a qualified engineer.
You'll need a long 4mm hex key, a Philips screwdriver, a 12mm socket, a spanner, and some pliers.
1. Fault Diagnosis
So your boiler has a burner lockout fault. In my case it was 9F 855. Others have 8F 855 or similar. Most tutorials indicate that this is a fault with the oil feed and advise bleeding air out the oil line or replacing the pump. However you might have a different burner-related fault.
Take a look at the front of the Riello RDB burner. The central reset button doubles as an LED which can flash fault codes. These flashes can tell you what type of error the burner is experiencing. In my case, it was flashing red and orange which indicated a fan motor error.
You can look up the fault code patterns in:
- Your boiler's installation manual [1]
- The Riello manual for your specific burner [2]
- A Riello fault finding diagram for your burner [3]
The manuals also suggest tests you can perform with a multimeter, e.g. ensuring the correct resistance across the motor wires or the capacitor etc. (however in my case these were all correct despite the control box being faulty).
2. Burner Removal
Removing the burner from inside the boiler is something I was unable to find in any videos online. It seemed daunting but is actually very simple.
First, before you do anything, electrically isolate the boiler. Close the kerosene/oil line. In my case, a ball valve was present on the oil feed behind the flexible hose.
Next, ensure your oil line has enough slack in it to allow the burner to be pulled out. If not, you may have to disconnect the hose after isolating the oil supply.
Remove the air intake tube by loosening the jubilee clip and pulling it up.
The burner is held in place by a single hex bolt. Undo this and carefully slide the burner out.
3. Burner Disassembly
There are several helpful videos online showing disassembly of the burner [4][5].
To remove the pump, start by removing the thumb screw and the solenoid (not shown in photo) from the brass piece atop the pump:
Next you'll need to remove the high-pressure copper oil line from the left side of the pump. This line delivers oil from the pump head into the combustion nozzle. It is not the same as the main oil inlet line (the flexi hose), which can be left attached to the pump at all times.
The pump is mounted to the fan motor via 3 x 4mm hex bolts. Undo those and pull the pump out (pump already removed in photo):
Make sure you don't lose the plastic insert which sits on the shaft of the pump.
Next, remove the motor capacitor. (Not pictured.)
Pull off the black plastic cap, and carefully remove the two spade terminals. If you can, discharge the capacitor by bridging the two terminals with the metal tip of an insulated screwdriver. Then unscrew the capacitor from its mounting point.
Note: the capacitor is non-polarised i.e. it doesn't matter which side of the capacitor each wire goes in.
Next, undo the two black fan casings to the right of the burner. These are also 4mm hex bolts.
This will expose the fan's impeller.
Important: Note the ~1mm gap behind the impeller: this gap is important when re-assembling it. The impeller should not touch the body of the burner as this would cause noise, grinding, or siezing of the fan as it spins.
To remove it, undo the 4mm hex grub screw then pull the whole thing off. Mine was very stubborn. I had to spray a small amount of silicone lubricant on the coupling and wrestle it off. (Alternatively, if your fan motor is already broken, you could undo its screws at the front and gently hammer on the shaft to knock the impeller free.)
After removing the impeller, undo the motor's bolts from the other side of the burner, and pull the motor free. You may need to remove the control box to free the motor wires.
Important: Note the thin rubber seal around the mounting face of the motor. Ensure you keep it there when re-mounting the motor.
4. Control Box
Removing the control box is straightforward so I won't detail it heavily. Basically, undo the two bolts holding the box in place. Remove all the terminal connectors from inside the box and lift it away.
There is a square seal, behind which are the wires for the high-voltage ignition electrodes. These are simply pulled away firmly with a pair of pliers. They look like they're held in by small Philips screws, but are not. When reattaching the control box make sure to re-establish the seal and don't pinch any wires.
5. Reassembly
Follow the above steps in reverse order. Make sure the control box wires are inserted firmly and correctly and that nothing is trapped. Make sure all seals are good, and ensure a 1mm gap behind the fan impeller.
Helpful Resources
[1] Worcester Bosch installation manual:
Greenstar Heatslave 2022+ installation manual | Worcester Bosch
central heating boilers, combi boilers, gas boilers, oil boilers, gas central heating, heating engineers, boiler installation, boiler repair
www.worcester-bosch.co.uk
[2] Riello RDB Heatslave burner manual:
[3] Riello RDB burner fault finding chart:
Riello RDB Oil Burner Fault Finding Logic - MO535-MPF
Troubleshooting guide for Riello RDB oil burners with MO535-MPF control box. Includes LED codes, anomaly types, and diagnostics.
studylib.net
[4] Riello RDB burner assembly:
[5] Riello RDB burner strip down:
Last edited:
So here is a tutorial on how to diagnose and replace parts on a Riello RDB type burner. I am not an expert but hopefully the following can prove useful to others in the future.
WARNING: Do not attempt any of this unless you are suitably competent. This is not intended as professional advice and is for educational use only. Oil-fuelled appliances can be very dangerous. Make sure you completely understand all the procedures you undertake. Pay particular attention to safety, esp. in relation to electrics, flammable liquids/vapours, and handling of harmful exhaust gases. If you're at all unsure, call a qualified engineer.
You'll need a long 4mm hex key, a Philips screwdriver, a 12mm socket, a spanner, and some pliers.
1. Fault Diagnosis
So your boiler has a burner lockout fault. In my case it was 9F 855. Others have 8F 855 or similar. Most tutorials indicate that this is a fault with the oil feed and advise bleeding air out the oil line or replacing the pump. However you might have a different burner-related fault.
Take a look at the front of the Riello RDB burner. The central reset button doubles as an LED which can flash fault codes. These flashes can tell you what type of error the burner is experiencing. In my case, it was flashing red and orange which indicated a fan motor error.
You can look up the fault code patterns in:
- Your boiler's installation manual [1]
- The Riello manual for your specific burner [2]
- A Riello fault finding diagram for your burner [3]
The manuals also suggest tests you can perform with a multimeter, e.g. ensuring the correct resistance across the motor wires or the capacitor etc. (however in my case these were all correct despite the control box being faulty).
2. Burner Removal
Removing the burner from inside the boiler is something I was unable to find in any videos online. It seemed daunting but is actually very simple.
First, before you do anything, electrically isolate the boiler. Close the kerosene/oil line. In my case, a ball valve was present on the oil feed behind the flexible hose.
View attachment 409903
Next, ensure your oil line has enough slack in it to allow the burner to be pulled out. If not, you may have to disconnect the hose after isolating the oil supply.
Remove the air intake tube by loosening the jubilee clip and pulling it up.
The burner is held in place by a single hex bolt. Undo this and carefully slide the burner out.
View attachment 409906
3. Burner Disassembly
There are several helpful videos online showing disassembly of the burner [4][5].
To remove the pump, start by removing the thumb screw and the solenoid (not shown in photo) from the brass piece atop the pump:
View attachment 409909
Next you'll need to remove the high-pressure copper oil line from the left side of the pump. This line delivers oil from the pump head into the combustion nozzle. It is not the same as the main oil inlet line (the flexi hose), which can be left attached to the pump at all times.
The pump is mounted to the fan motor via 3 x 4mm hex bolts. Undo those and pull the pump out (pump already removed in photo):
View attachment 409911
Make sure you don't lose the plastic insert which sits on the shaft of the pump.
View attachment 409912
Next, remove the motor capacitor. (Not pictured.)
Pull off the black plastic cap, and carefully remove the two spade terminals. If you can, discharge the capacitor by bridging the two terminals with the metal tip of an insulated screwdriver. Then unscrew the capacitor from its mounting point.
Note: the capacitor is non-polarised i.e. it doesn't matter which side of the capacitor each wire goes in.
Next, undo the two black fan casings to the right of the burner. These are also 4mm hex bolts.
View attachment 409914
This will expose the fan's impeller.
Important: Note the ~1mm gap behind the impeller: this gap is important when re-assembling it. The impeller should not touch the body of the burner as this would cause noise, grinding, or siezing of the fan as it spins.
To remove it, undo the 4mm hex grub screw then pull the whole thing off. Mine was very stubborn. I had to spray a small amount of silicone lubricant on the coupling and wrestle it off. (Alternatively, if your fan motor is already broken, you could undo its screws at the front and gently hammer on the shaft to knock the impeller free.)
View attachment 409913
After removing the impeller, undo the motor's bolts from the other side of the burner, and pull the motor free. You may need to remove the control box to free the motor wires.
Important: Note the thin rubber seal around the mounting face of the motor. Ensure you keep it there when re-mounting the motor.
View attachment 409915
4. Control Box
Removing the control box is straightforward so I won't detail it heavily. Basically, undo the two bolts holding the box in place. Remove all the terminal connectors from inside the box and lift it away.
View attachment 409916
There is a square seal, behind which are the wires for the high-voltage ignition electrodes. These are simply pulled away firmly with a pair of pliers. They look like they're held in by small Philips screws, but are not. When reattaching the control box make sure to re-establish the seal and don't pinch any wires.
View attachment 409917
5. Reassembly
Follow the above steps in reverse order. Make sure the control box wires are inserted firmly and correctly and that nothing is trapped. Make sure all seals are good, and ensure a 1mm gap behind the fan impeller.
Helpful Resources
[1] Worcester Bosch installation manual:
Greenstar Heatslave 2022+ installation manual | Worcester Bosch
central heating boilers, combi boilers, gas boilers, oil boilers, gas central heating, heating engineers, boiler installation, boiler repair
[2] Riello RDB Heatslave burner manual:
[3] Riello RDB burner fault finding chart:
Riello RDB Oil Burner Fault Finding Logic - MO535-MPF
Troubleshooting guide for Riello RDB oil burners with MO535-MPF control box. Includes LED codes, anomaly types, and diagnostics.
[4] Riello RDB burner assembly:
[5] Riello RDB burner strip down:
Now you couldn't ask for more of a guide than that.
Good for you for making the effort... Next, your own youtube channel
I doubt it! I tinker with electronics and other engineering but I've not done much with boilers until recently.
Unfortunately after all this my boiler is still exhibiting pressure issues which is what started my experiments in the first place. (Pressure loss every day, pressure spiking during heating, PRV passing etc.)
The only thing I haven't replaced is the expansion vessel so I suppose that's next on the list. The contents of my wallet are quickly disappearing to the local plumbers' merchant.
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