On Mon, 03 Dec 2012 10:44:49 +0000, MM wrote:

Spark

Would one hear that sparking?

Possibly, the noise of the fan can mask it.

There IS no fan noise! There is *no* noise of any kind. The LED on the
DKO970 comes on. That's all.

Because it's gone into lock out.

When the boiler starts successfully (on its own), the LED does not
come on at all. There are a few seconds which elapse since the Danfoss
timer triggered its ON event, then the fan starts, then a few seconds
later the burner starts and everything is hunky dory.

That is to be expected, the time switch ON is probably opening a valve
some where, this takes a few seconds, the auxillary switch in the valve
then turns the boiler on when the valve is open, the boiler should then
start it's ignition sequence of fan on for 10 s or so, spark, ignition,
flame detection, run...

But it's when the boiler *does not* start, that's when there is NO fan
noise, no other noise, no other signs of life -- and then the LED
comes on and stays on.

Because it's in lock out.

It's when the fan doesn't start and the LED comes on, that's the
mystery.

You have that arse about face the LED comes on because the boiler is
latched into lock out. The fan won't run in this state until the reset is
pushed.

He checked for no water in the tank, but the actual line itself has not
been removed/blasted through. Perhaps it should?

Well as virtually everything else has been changed or looked at there is
little else to do, I doubt it's the motor capacitor, if they go the motor
just won't run or will be horribly noisey.

I'd get him to throughly check the fuel line from the tank isolation
valve, open that with the outlet disconnected to get a good flow into a
bucket to flush any debris out of the valve. Then look at and clean every
item and pipe. This will require a complete dismantling to check for a
bit of crud on say the inlet of the filter. Remember what I said about
bits taking a while to be drawn to where they cause a problem and then
falling back. Just beacuse the inlet to a device is clear when you look
at it doesn't mean there isn't a bit of crud way back down the feed
pipe...

The motor, however, hasn't been changed. Allan Mac just now mentioned
a possible problem with a 'tight' spot on the motor bearings.'

Not likely IMHO.

As the boiler starts and behaves everytime the lockout is cleared I
don't think there is anything fundemental wrong with boiler. It looks
as if tt's going into lockout at some random/indeterminate period
after running for a while. This could be a fault in the shutdown
procedure, does the boiler have a permenant live or just a single
"call for heat" live? I don't find that very likely TBH.

I don't understand that last question. Don't have the technical
knowledge.

How many wires feed the bolier just live, neutral, and earth or is there
an extra wire that becomes live when the time switch is on and any room
stats calling for heat?

--
Cheers
Dave.