Thermistor testing

[jackecole]

Just a quick question: when testing a thermistor as suspected faulty - obviously the resistance will drop as the boiler temperature rises, but my question is this: how do you do it quickly enough, as you need to remove the leads to it to test resistance (ie with no power to it) and if you remove the wires the boiler temperature will cool down by then!..... ??

 

[Agile]

You seem to want us to train you to fix boilers when you are not gas registered!

If the thermistor is reading the right value when tested then its probably OK.

Very rarely they go open circuit when hot but normalise as they cool.

The boiler perhaps loses 1°C per minute when the burner goes off during heating or if the pump is stopped so its fine to measure the resistance when the boiler is still hot.

Tony

 

[jackecole]

Hi Agile - I'm on a gas training course now and have a porfolio to complete in and out of the training college. I've also got written exams coming up in approx 2 months time!!

I was just querying about thermistors after reading various posts.

They seem a common fault.

Is it correct that an open circuit/or 0 resistnce means they are faulty...

 

[Agile]

But you have already posted about numerous boilers with faults that you are apparently trying to fix.

Most annoying is that you say they are YOUR boiler as if you are a DIYer trying to fix then for yourself instead of the reality that you are an illegal non reg.

 

[tamz]

But you have already posted about numerous boilers with faults that you are apparently trying to fix.

Most annoying is that you say they are YOUR boiler as if you are a DIYer trying to fix then for yourself instead of the reality that you are an illegal non reg.

Getting in a bit "work experience"

 

[Agile]

Proper "work experience" is meant to be under the supervision of a registered engineer.

This fellows obviously doint it himself for customers otherwise he would be able to ask the supervising engineer.

Not only is that illegal but totally unfair to the customers and gives our trade a bad name.

Customers, protect yourself from people like this by NOT letting them touch your boiler unless they can show you their gas-Safe photocard.

 

[DP]

jackecole, o/c or 0 resistance would indeed indicate defective thermistor.

 

[jackecole]

I must point out, to Agile, and anyone else who hass read this post: I honestly do not do boiler work/repairs or anything of that nature. I am just trying to learn and am sorry for asking silly questions that make you think otherwise.

I was just querying a point that I was a little confused about after reading this site/combi books.

Sorry for the confusion.

I also agree, do not allow ANYONE to attempt ANY BOILER WORK/GAS WORK withotu seeing their gas safe card.

 

[onlyfitidealboilers]

what happens if it is a PTC & not an NTC thm bit of homework

 

[DeltaT]

jackcowboy, I don't normally help CC/CCCs, but here's a wee tip for you;
Get yourself an autorange multimeter, a great piece of kit for boiler repairing & fault finding.

http://www.temperatures.com/thermistors.html