Feroli Sigma thermister peculiarity

[Paul Barker]

Went to a sigma 60-100 gc 41-267-19

no life, and not sending live feed to pump. Measured thermister to eliminate it from my enquiries as many pcb's won't go on to anything if thermister is out of range at the start, and it was over 1.5meg. Emailed Ferroli who responded

"thermister should be 1 meg, if not 230v from grey lead on X5 it's thermister or pcb."

So I took a 1 meg resistor to job, replaced thermister with it, and boiler worked, let it get warm.

Then the funny thing, put thermister back in circuit and it's now working.

My thoughts are that the change in temperature I forced by starting the boiler on a resistor has kicked the thermister into life. I presume though that it is a knackered thermister and shall get one on order right away.

Does this sound familiar?

 

[Gasguru]

In a moment of boredom (and to see why parts fail) not far back I dissected a thermister off a Glowworm Compact (the customer had been having intermittent faults for months).

The resistance was eratic at one particular temperature.

After carefully cutting away the potting compound I came across a standard bead thermister, the leads were soldered onto a standard pcb header to enable connection the the flying lead.

The leads were badly oxidised and the quallity of the soldering was abysmal.

Perhaps it was made with child labour in China. I thought as a minimum standard the connection would utilise spot welding or ultrasonic welding.

I'm amazed they left the factory in such a state.

 

[Agile]

I had an odd one a few days ago!

At room temp it was about right but it went DOWN to the 60 C resistance at only 40 C so the hot water was way too cold as it turned off the gas.

Tony