The lockouts ONLY occur approx 20 to 30 minutes after first switch-on! AND THEN NEVER HAPPEN AGAIN while there is a "call for heat"!
The Danfoss programmes were set to: 04:30 to 07:30, 16:00 to 17:30 and 21:00 to 22:30.
I have kept a careful record of the boiler lockouts since October.
While reviewing this record (about 12 sheets of A4 by now), it became obvious that the lockouts only happen (and NOT always) after the boiler has come on from stone cold.
Here is a summary:
05/Dec/12: Started at 16:00. Locked out at 16:30. Reset pressed. Ran fine to 17:30 Ditto 06/Dec/12: Started at 16:00. Locked out at 16:20. Reset pressed. Ran fine to 17:30 Ditto 06/Dec/12: Started at 21:00. Locked out at 21:20. Reset pressed. Ran fine to 22:30 Ditto 07/Dec/12: Started at 04:30. Locked out at 05:00. Reset pressed. Ran fine to 07:30 Ditto 08/Dec/12: Started at 16:00. Locked out at 16:25. Reset pressed. Ran fine to 17:30 Ditto 10/Dec/12: Started at 04:30. Locked out at 04:50. Reset pressed. Ran fine to 07:30
So yesterday I had the brainwave (well, I thought it was!) of switching the Danfoss to permanently ON (it's a CP15 and has the settings ON, OFF, AUTO, ALLDAY), figuring that I'd only need to press the reset button the once after the first 20 - 30 minutes and thereafter the boiler would continue to run.
And this is exactly what has happened since yesterday morning at 07:30!
Yesterday morning I switched the Danfoss to ON (i.e. 24/7) and the boiler started. True to form, it locked out at 07:55, i.e. about 25 minutes later. Then I pressed reset and the boiler has been running EVER SINCE!
I have adjusted the temperature of the house by use of the Honeywell TRVs. So right now, at almost ten to seven on Friday morning I have a lovely warm house and the boiler is still running fine. Not a single lockout since that first one yesterday morning at 07:55. It's been running without problem for roughly 23 hours.
Now, which one of you can possibly diagnose why it only locks out after the boiler starts up the first time from stone cold and comes to temperature?
Beats me. Beats my heating engineer. Beats even HRM Wallstar, who have been consulted by my heating engineer several times (he knows several engineers there personally).
It's a puzzle and no mistake.