Danesmoor 20/25 RS problems

[dickmct]

My self-installed CH system has broken down after 11yrs fault-free running.

The system is sealed with a Danesmoor 20/25 RS floorstanding oil boiler controlled by a Honeywell Y plan. Firstly the 3-port valve motor failed, shutting down the system. I replaced the motor unit which fixed the problem for a few hours. Next symptom was boiler lock-out: resetting gets the fan running but lock-out again occurs after about 13 secs. There is oil arriving at the pump but no discharge; the photo cell is clean; there does not seem to be any spark at the igniter. I looked at the transformer and HT leads and found that the HT leads had been crossed since manufacture and had shorted out at the crossing point. I checked the transformer coils and found that both are not conducting.

I assume from these symptoms that the transformer has burnt out and since there is no ignition the fuel solenoid is not openning. If I am right a change of transformer and new HT leads should sort things out. Is this correct? Could other damage have occurred? Is there any other reason for this to happen? What else should I check?

Any help would be very welcome,

Many thanks in advance.

 

[Terrywookfit]

It would be helpfull to know boiler /burner make and model!
It might be a good idea to have it serviced by someone who understands how it should work!

Its nearly xmas so why not treat your long abused companion to a make over !!

 

[dickmct]

Terrywookfit,

Thanks for the reply. As stated it's a Worcester Danesmoor 20/25 floorstanding roomsealed unit. The burner is an Electro Oil Inter B11 with a Danfoss EBI transformer. a Danfoss BFP 11L3 pump and a Satronics TF 830B controller, all of which seem to be industry standard units. I have the boiler insallation and servicing manual so can do most things myself(I like the challenge). With this post I am asking for advice/confirmation on my diagnostics before I go out and spend money. I take your point about buying in expertese but we are enjoying a building boom up here and plumbers/CH engineers are hard to come by.

 

[Terrywookfit]

Have you checked for voltage at the ign txfr ?
You can also bridge the connection in control box !!
Its quite possible that the EBI has blown the control box as well!!

When you get it working check to make sure the burner is not short cycling as this will overheat EBI and cause it to blow again!!

 

[dickmct]

Thanks for the tips.

I've not yet checked for supply to the txfr but will do so ASAP.

"Bridge the connection in the control box"- does this mean the txfr mains terminals? Would this lead to oil delivery to the nozzle followed by lock-out due to flame failure sensed by the photo-cell?

As I said in the first post the HT leads had been crossed at the bottom of the electrodes (pressumably since manufacture) and the insulation has burnt through so shorting out the HT coil. Have you seen this before? Both coils are now dead when tested with a multi-meter 'though the txfr shows no signs of over heating.

Before failure the burner was not short cycling as far as I know. I will check for this as the EBI is only for intermittent ops.

 

[dickmct]

Monday afternoon.

I've changed the txfr, ordered new HT leads and cobbled up the old ones mean time. Ignition first time! No short cycling, no other probs yet. I'll see how it goes.

Many thanks.

 

[Agile]

Did you measure the resistance of the HT coil on the new transformer?

Sometimes people test them on a low range without realising that they can be as much as 5K or 10K.

Tony

 

[dickmct]

Hi Tony,

I did a brief test of the new coil before fitting; it was about 4-5k on each side. and it's now in and running. The old coil gives 8meg on the primary and 3.4k on the secondary so it seems that the old primary had broken down when the HT leads shorted out. Has anybody else seen shorted HT leads like this before? I am lucky that there was no other damage, especialy to the controller.