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URGENT Grant Combi 70 MK2 won't fire

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Robert Tyrrell

Robert Tyrrell

Gas Engineer
Messages
699
I've fitted a completely new burner to a Grant Combi 70 and the motor will not run (so consequently the burner won't fire) despite there being live 230v power to the control box.
I have read the wiring diagrams and even spoken to Grant themselves but I cannot get to the bottom of the problem so if anyone can help I would appreciate it.
There is power all the way through to the control box, I know because I've checked each and every connection.
The only thing that isn't working as it should is the 'Boiler On' neon but I cannot see how that would stop the boiler from working.
I should add that I also took the microswitch assembly apart and promptly dropped all the bits so I have no idea which wire connects to which part of the switch now and there are two of them. The power does flow through the switches and the diverter valve is causing the switch to activate.
I've attached the wiring diagrams and an image of one of the microswitches - My understanding is that power comes in on one and out on 4 but I'm now just thinking that it might be the actual microswitches themselves (although why two would go at the same time is intriguing).
I can, and do, sort out my own electrical problems b ut this has got me stumped but it might be more to do with the fact at I had my second jab yesterday and then did 3 hours martial arts training.
All positive help appreciated.
Screenshot 2021-05-26 at 15.25.35.png
 

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If you have power to control box during a demand then the fault will lie on the control side.
What tests have you run?
I have no idea what you've done to the other wiring.
 
SJB060685 said:
If you have power to control box during a demand then the fault will lie on the control side.
What tests have you run?
I have no idea what you've done to the other wiring.
Click to expand...
Thanks - I know it's on the control side but I just can't work out where and if you've ever seen one of these you'll know what a nightmare it is to work on. You have to virtually dismantle to the casing completely as you can't get to the wires because of how they're routed.
Cheers anyway
 
SimonG said:
Why did you change the burner?
Click to expand...
Because I wasn't certain if it was operating properly and I was trying to get this done quickly - it's a holiday cottage (currently being let as well) and I do all this guy's properties but this is the only one with an oil boiler.
I have to repair it every year without fail.
Besides - I had a spare burner just for this sort of situation anyway
 
Ok.
If you have 240 volts to box, which you said you do then start sequence and see if you have 240 volts to motor.
If you do and its not turning over then you could have seized bearings (entirely possible if the burner has run for some time), or a tight spot on the pump (again entirely possible). Capacitor could be weak as well mate.
 
Ok. I was misreading your comments. I thought you were Implying you had 230 volts at the burner control box. You need to determine if you have voltage at the burner control box first. If you do then it's burner related, if not then the problem is on the main board somewhere.
 
Robert Tyrrell said:
The only thing that isn't working as it should is the 'Boiler On' neon but I cannot see how that would stop the boiler from working.
Click to expand...
If you look at your diagram both the burner and the 'boiler on' neon get their neutral from terminal 11. So, my guess is that you've lost the neutral somewhere before it arrives at 11. There's a link between 2 and 3 on the diagram, is it in place?
 
Last edited:
Chuck said:
If you look at your diagram both the blower and the 'boiler on' neon get their neutral from terminal 11. So, my guess is that you've lost the neutral somewhere before it arrives at 11. There's a link between 2 and 3 on the diagram, is it in place?
Click to expand...


The blower 😂😂. He needs to determine if he has a live and neutral at the control box. If not then work your way back from there.
 
Robert Tyrrell said:
Because I wasn't certain if it was operating properly and I was trying to get this done quickly - it's a holiday cottage (currently being let as well) and I do all this guy's properties but this is the only one with an oil boiler.
I have to repair it every year without fail.
Besides - I had a spare burner just for this sort of situation anyway
Click to expand...

I was wanting to know what the original problem with the burner was.
So the spare burner, is it brand new?
 
Thanks for the assistance guys:

Simon G - The spare burner is brand new - straight out of the box so I really don't think that there's a problem at the burner end, and as far as I can remember, it does have 230 at the live on the control box so I think it's more than likely to be the controls. I just can't work out where because it's been running as it is for years - although I have been called out to repair it nearly every year since I took it on in 2016 (and service it as well btw).
It has a remotely operated heating stat as well. I'll have to look at where that's plugged in and check the link between 2 & 3 as Chuck mentioned.
I'll have to take all this advice with me on Friday when I go back :)
 
If you have 230 volts at the control box then the fault has to lie within the burner. Power is only sent to the burner when theres a demand and stats allow it.
 
Update on this vexing problem.
I'm not really sure what happened but - I was on the phone with Grant support and the lockout light appeared. I pushed it and the burner fired.
I have no idea why it didn't do this before though and still don't although I have been through every terminal and link a few times so it might be that I tightened something that was loose. the neons still don't work either but I think that they've just expired and need replacing but they won't stop it working so I'm not in a hurry to sort that particular problem.

I now have a new problem with the burner in that there is no oil getting to it.
I do think I know what the problem is though and I'm going back in the morning to check the tank filter. I might have to employ the suction pump to draw it through as well because it's almost on the same level as the burner and there's only half a tank of oil.
 
Start at the tank and move in methodically. Check tank strainer and any filters/fire valves etc to the flexi hose. Run a few litres off at the flexi to prove you have decent supply of oil to the burner. If you do then the problem lies on the burner.
The tank at same level as burner on a gravity system is not a problem, even if you have half a tank left.
 

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