On 4 Dec, 12:26, MM wrote:
Snip

On one occasion the lockout happened after about 30 minutes into the
cycle. Another time the boiler ran for about 1.5 hours and then
lockout occurred.

Usually, however, once the boiler has started, it will run to the end
of the desired period.

When I say "run", I mean that its typical behaviour is to come on,
burn for about 15 minutes, then switch off. It then waits for around 4
minutes and then comes back on for only a few minutes, provided the
cycle specified by the Danfoss programme is still active. The boiler
will thus switch itself ON and OFF numerous times during a long "call
for heat" cycle.

If any part of the above isn't clear, let me know!

Thanks for your response BTW.

MM- Hide quoted text -

- Show quoted text -

Hmmm....

As I said, I am no expert either, but I begin to suspect either the
Danfoss, or else the moterised valvery gubbins.
Maybe as an earlier poster suggested they aren't switching cleanly.

But the intermittant nateure of the problem is an embuggerating
factor.

Could you wire up a plug in (or some other form) of timer as a
temporary supply to the boiler and pump and switch it on and off a
number of times and see whether you do or don't get lockout? If it
locksout, then it's probably not Danfoss/Valve(s) if it does, then...
well, you're probably no further on.

Chris

Do let us (and future generations) know what it was when you've solved
it.