white paste from thermistor pocket?

[biglofty]

Hi there could any one give me some answers.
I visited a job yesterday, the boiler was a baxi 80e it was operating on CH & HW but on low flame, the boiler still operated when the temperature gauge was turned right down, at first i thought it was the thermistors but they both gave the correct reading on the multimeter. I was inclined to think that i was the pcb not sensing the temperature fluctuations though the thermistor. Any way i changed the thermistors on CH & HW on removing the CH thermistor i found it covered i a white paste type substance. I installed the new themistors and hay presto everything worked. I have just moved down to kent from yorkshire and i'm still trying to get used to all this hardwater down here and the problems it can cause. Would the white paste be the calcium in the water that has perhaps reacted with the inhibitor in the CH system, i thought the calcium would be hard and coat everything.

1st time user - I found all the information on the other topics very good. sharing info is a great idea, if it saves time and customers money.

 

[Onetap]

Would the white paste be the calcium in the water that has perhaps reacted with the inhibitor in the CH system, i thought the calcium would be hard and coat everything.

It's heat transfer compound, a thermally conductive paste used to ensure that there is heat conducted from the flow pipe to the thermsitor. If they're just clamped together, there will only be a small area of metal-to-metal contact and so limited heat transfer. Sold in electronics shop as heat sink compound.

Why does a Corgi registered boiler technician need to be told this?

 

[bripl]

Why does a Corgi registered boiler technician need to be told this?

just a few points
1/ no such thing as a corgi registered boiler technician
2/corgi is the holder of registered gas business's
3/gas is such a large field no one person knows it all so you have installers, you have service engineers ,you have breakdown engineers, you have domestic/industrial/catering/mobile homes/mobile catering/atmospheric/blown/lpg. all different elements you may find someone who can install but cannot fault find or you may find some one who can dabble in a few of the above but not carry out repairs.as for heat paste very few installers would need to know about it but a service/breakdown engineer would be familiar with it. :roll horses for courses and all that

 

[biglofty]

thanks for coming back.
it was my understanding that the conductive paste would be used in dry pockets, not wet pockets. This still doesn't explain why the thing worked!

bripl was spot on, my experience is limited to fitting work - banging systems out, a few faults and some servicing work, the company i worked for had guys that only dealt with faults so you never get the experience, i left the company to do something else but decided to get back into gas work a few months ago.

I attended various manufacturers training courses, but they are poor for giving advice on common faults because it make their boilers look bad.
The other engineers on the courses i have attended are in the same position as myself, fault finding interests me because my knees are knackered.

 

[bripl]

i do believe the 80 is the same as a 105.the sensor is in a dry pocket so it will be heat sink compound.the best technical advice for boilers is available on argi .

www.argi.org.uk it will not let me post the address just do a search on argi and join up if you have not already

 

[esra_ptrap]

The paste is actually silicon based and so would work in a wet environment ... Never seen it used in one though

 

[Agile]

Its probably zinc oxide powder in a silicone grease or something similar. Easily available at a Maplins.

Its most often seen on overheat stats when clipped to the outside of a flow pipe and should always be replaced.

If you have not got any with you then you can use silicone grease in an emergency but get some if you are going to do repairs and servicing.

Tony