HRM Wallstar - control box swap and spark generator transformer inspection

I have been having issues with my HRM Wallstar oil boiler locking out, usually first thing in the morning.  One of the common issues that was mentioned is the control box.  This sits inside the burner unit under the outside cover of the unit, and has the lockout reset button on it. I had also read that the TF series control boxes had a tendency to destroy the Danfoss EBI spark generator/transformers on these units.  This is indicated by the transformer casing being deformed and having a 'bump' at the top.

So let's get inside the boiler and have a look.  First things first, turn off the power supply to the boiler at the switch.  We then need to go outside and remove the front cover by slackening off the four screws on the sides of the cover and lifting it up and off

Next step is to unscrew the red burner cover which has a single plastic screw holding it in place

The control box will be obvious on the front of the burner, it has a small screw holding it in place, and then just pulls out.

The spark generator transformer is located behind the wiring base located behind the control box, which can be removed by undoing the two allen bolts.

Once these are removed you can push the wiring base out of the way and pull the spark transformer out to check for deformities or the tell tale bump, fortunately my unit was fine.

A visual inspection of the Satronic TF 830B indicated that it's likely this is the original unit, which would have been installed in 1997, so it has had a pretty good innings.  As far as I know there's no real way to test these units, and most people (including engineers) just try swapping them and seeing if the problem goes away.

It turns out there is a later control box, the Satronic DKO 970 which is pin compatible with the TF 830B.  Apparently the issue of destroying the Danfoss EBI doesn't happen with this later version, so I started hunting round for one, and managed to pick one up for a sensible price on eBay.




On checking the wiring diagrams for both units, it appears the DKO 970 also has an extra pin which gives the ability to wire in an external reset button for the lockout function, which would be incredibly handy considering how inaccessible the current one is.  It also has a feature to give flash codes to give the cause of the lockout.  You can see from the pictures, the DKO unit uses plastic cased relays whereas the older unit uses open relays which I imagine are more prone to dirt ingress and failure.

To swap the spark transformer, follow the above procedure to gain access to it, then disconnect the existing one from the wiring base, and wire the new one up, then refit is the reverse of removal.  To swap the control box, it's just a case of following the disassembly procedure to inspect and remove the old control box, push the new one into place, and tighten the screw.

Once done, we need to fire up the boiler and check everything still works.  I decided to prove the lockout function by removing the photocell so the control box would not see a flame.

Once this was done, I turned the power back on and operated the override switch at the very bottom of the unit which forces the boiler to start. As expected, the unit went into lockout quickly. With the photocell back in place, I pressed the reset button the control box, and it fired up fine.  Last thing to do is to turn the power back off, put the override switch back into its normal position, and put the covers back on before turning the power back on.









I will write a future guide on how to add a remote lockout indicator/reset to the front panel of the boiler on the inside, which is much easier to get to.  I've got big plans for the winter to rig up a Raspberry Pi to alert me when the boiler goes into lockout, which will hopefully stop the big surprise of cold water in the morning when you expect hot!



Parts required to do this:-

Honeywell Satronic DKO 970 control box

Danfoss EBI4 spark generator transformer - cheapest I found was on eBay so have a look there