Thermistor replacement - just a band aid ?

[martygturner]

As per life's rules boxing day boiler problems.

Baisi - m110.32 /sm/e - intermittent hot water, central heating only getting slightly warm unless turned up to max then over hot with bit of dribble passed out the prv.

Called out an engineer and diagnosed the problem as a faulty CH temp thermistor as that what the self test lights said - middle coming on to red with right hand blinking. All fixed, replacement + a spare ( plumbbase sold them as pairs or that's what they had in stock - who cares) all told £115 which over Christmas was not bad.

But have I just paid for a band aid ?

The engineer left the old and the spare - their is a marked difference between the two - the old one is brass with a point, it had a buildup of black on it and the new one is stainless with a flat end.

The readings from the two are at 22 degrees : 10300 ohms old and 9900 new....not exactly a huge variation....but the boiler is back to working.

The system was drained and refilled in the summer with a good inhibitor at its service....

So just a faulty sensor or is it worth getting a bit more digging done ?

 

[martygturner]

I have just answered my own question...once heated the old thermistor stopped at 4000 ohms or 50 degrees so the moral of that story is check the range of them not just a static reading.....see too much time on my hands.

 

[AGAS]

Thermistors go faulty at high temps so static readings are useless , when static they show as faulty when open circuit