On Tue, 12 Jul 2016 22:04:52 -0000 (UTC), Tim+
wrote:

T i m wrote:
On Tue, 12 Jul 2016 21:30:01 -0000 (UTC), Tim+
wrote:


or failing pump
probably.

It's yer classic Grunfoss 3 speed and sounds like it running ok (and
again, you have a good flow round the system).

Not unknown for impellers to come adrift of the motor shaft or just get
eroded away through corrosion/cavitation. But if pipes are heating up
quickly downstream after firing up then probably okay.

Check.


Okay, I'm out of ideas. ;-)

Yeah, me too, apart from taking some measurements and seeing what I
find ('you can manage what you measure' etc).

My background 'fear' is there is nothing wrong with anything and that
the upper limit stat has just got weak?

It's just that it seems to be in a god place to protect the boiler
from melting down in the event of a total water loss (where you may
not get an overtemp reading further up the flow path)?

Subject to the tube that carries the overtemp stat not being
compromised (and I think from memory it may / should be attached to
one of the main exchanger tubes) and not being able to get a
replacement, maybe I could use a thermistor [1] and a little PCB
driving a relay make something more 'adjustable'?

Cheers, T i m

The thermistor and wiring run at 205 DegC on our 3D printer 'hot end'
so the temperatures experienced in the boiler shouldn't be an issue.