Danfoss BHO 61 controller/ burner

[cwmmeilwch]

Hi I am hoping for some advice on a problem I am having with my trianco central heating boiler. It has been running fine but today went to lock out. Reset, and it fired up for a few seconds then lock out again. After a couple of attempts would still reset but then not fire at all. Check oil supply to pump, fine. Check electrodes, good continuous spark. Check light sensor, all clean then put a meter on it, got a changing reading from light to dark. Disconnected oil supply line from pump to nozzle...no fuel at all. This model has a coil/solenoid on the back of the pump. I presumed this was an electro magnetic control to open/shut the fuel off from the pump. Put a meter across the coil and it appears ok, not an open circuit but showing a resistance. So in my wisdom I put a permanent magnet on the end of the spindle and got a result, fuel and ignition. Take the magnet away and it all stops and goes to lockout. Am I looking at a control box fault or a coil fault? As it's an old system I appreciate it will need updating, we plan to install a new boiler later in the new year when all the building work is completed but need to keep this one running for a while. I have looked up replacement control boxes but it seem a bit confusing. My Controller is a danfoss bho61 and the pump is a dunfoss msla032. Any help or comments much appreciated. Thank, Tim

 

[outinthestix]

Can you check if the c.box is supplying voltage to the coil. Run the burner through to lockout while testing. If 240v present the problem is with the coil. If not its the box. If you don't have a non contact type voltage stick then with the power turned off cut the coil cable in two and piece them back together with a choc block. You now have somewhere to check voltage with your multimeter. Stix.

 

[cwmmeilwch]

Thanks outinthestix, will give it a go tomorrow and let you know what I get.
Tim

 

[spraggo]

Hi . Thank, Tim

The fault points to a faulty solenoid coil, it is not always possible to check these with a multi meter as in many cases they only short circuit when voltage is applied. The best way to check it is to remove it from the pump, insert a twist drill in the centre hole and start the boiler, after a few seconds you should hear a click from the control box and if the coil is OK you will feel that the drill has magnetized. Failing that happening fit new solenoid. On the other hand if OK there is a possibility that the drive pin that turns the cogs inside the pump have sheared resulting in pump failure, as the spindle will turn without turning the pump mechanism.

spraggo

 

[cwmmeilwch]

Hi Spraggo,
I initially tried what you have suggested but got no pull from the coil, there certainly wasn't any click from the control box, hence my permanent magnet experiment. What are the chances of finding a replacement coil for this age of pump? I did strip the pump to check the drive and all seems in very good order, coupling is good as well. Thanks for the help,
Tim

 

[cwmmeilwch]

Tried the coil today, put a meter across the leads and got no response at all so assume the controller was not putting out the voltage. To double check this I jury rigged a slave voltage to the coil which then worked and the boiler fired up. It then went to lock out again after about 15 seconds and on checking the controller there was a fair amount of warmth being generated through the side of the casing where what I assume is a bi-metallic device of some sort. I have ordered another replacement controller today a this seems to be the next move. Thanks for all the help and advice on this problem, I hope the new unit does the trick.
Tim

 

[spraggo]

Thanks for all the help and advice on this problem, I hope the new unit does the trick.

Tim

Well done, just to sum up the lockout mechanism would activate as it would be sensing a open circuit in the solenoid coil because it had been disconnected. If needed you can obtain a solenoid coil from.
http://www.heatingworldofspares.com/PublishedService?file=page&pageID=9&itemcode=MSLACOIL

spraggo

 

[cwmmeilwch]

I tried to work that out...why if the boiler had fired up it was locking out again, but sometimes it takes someone with a bit more logic to point out the obvious! Thanks Spraggo

 

[RobByass1]

I had a similar problem and it turned out to be the photocell - they get tired and start to fail intermittently, working for days at a time then not. The boiler will light up and run for a few seconds. The control box will lock out the oil valve solenoid if it doesn't receive a strong enough signal from the photocell. Check that the cell and the hole it goes into are clean first. The photocells are under £20 or perhaps you could borrow one? I cannot gurantee that this is the solution as there are so many possibilities, however replacing the photocell is the simplest and cheapest

 

[cwmmeilwch]

It turned out to be the controller! I sourced a replacement model that although different just required a few minor wiring modifications. It came with a new photocell so I fitted this as well even though the original was still working. Boiler is up and running fine, thanks for everyone suggestions and all for under £80.