On Tue, 19 Nov 2013 13:49:36 -0800 (PST), Calvin
wrote:

Hi,

My WallStar oil boiler (through-the-wall but otherwise conventional, non-condensing, not "system") has developed a fault which I feel is probably easy to fix if someone can help me understand how it's meant to work...

It locks out at some point but then is quite happy to start again if I press the lockout button (inside the outer cover on the burner itself). I've been "playing" and I get the feeling that it behaves itself better if the temperature control is set lower, although at the moment that's just my impression.
I wondered if the flow rate might be compromised somehow (maybe pump going faulty) but I can't hear any kettling.

Any ideas or pointers anyone? Please.

Be prepared for some heavy reading, Calvin! I was exactly where you
are a year ago. I'm digging our the Usenet links right now. It was a
veritable litany of problems that persisted off and on for six weeks
until the boiler was fixed. By the way, you don't state what model of
Wallstar yours is. Mine is a Wallstar 55 and approximately 10 years
old.

Watch this space!

MM