Thermister replacement


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Old 03-15-10, 08:03 AM
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Thermister replacement

Hi Anyone,
I'm new to the site, please help.
I have a Glowworm 38cxi combi boiler. My hot water goes cold after a couple of minutes, central heating seems ok. The boiler switches off and shows F14, a fault I am led to believe is with the domestic hot water thermister. Is this the likely cause of the fault?
I have ordered a replacement themister.
Is this part relatively easy to change? Any ideas or tips to look out for/ likely problems? I assume I need to drain the boiler and shut it down! Is this job beyond DIY?
Any advice would be much appreciated.
Thanks
 
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Old 03-15-10, 11:10 AM
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I personally have never seen one of these boilers.
Do you have your owners manual see if there is a number or email address to contact them. Ask then specifically what Fault code F14 is and what resistance value range should the thermister read. IF you have any electrical friends with an ohm meter you can verify if you have a defective sensor.
Also ask them if the sensor is in a well, which it probably is to prevent draining the boiler. At the very least if you do change it let the boiler cool down first.
 
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Old 03-15-10, 04:05 PM
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I'm suspecting this is a UK installation... that's why we're not familiar with that particular boiler... they do things a bit differently than we do here in the colonies.

But Luke's idea to measure the thermistor is a good one, and also to RTFM!

OK, I took my own advice and decided to see if I could find the manual... I did:

Glow Worm manual

It doesn't appear that the F14 fault you are seeing has anything to do with the domestic hot water... that fault is telling you that the boiler water temperature is above 95C ... so either the thermistor is bad, or there is another problem. I wouldn't assume that the thermistor is bad right off the bat, I would first verify if the boiler is overheating, and the thermistor is doing what it's supposed to do.

In fact, there are completely separate F-codes for faulty thermistors...
 

Last edited by NJT; 03-15-10 at 04:20 PM.
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Old 03-15-10, 04:39 PM
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Like anything else, thermistors can fail. But they are solid-state devices and are quite reliable.
 
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Old 03-15-10, 05:59 PM
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looks like in the manual Central Heating thermistor is 10k ohms @ 25C .
NJ Trooper nice find on the manual
 
 

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