Potterton Netaheat Profile boiler tripping

bathjobby · 3 Mar 2005

I have a potterton Netaheat Profile boiler circa 1989, gravity fed how water and pumped CH, flushed and treated in last 12 months.
The safety cutout trips intermittently (can go for days without tripping, others it will trip 2 or 3 times) on the boiler but I suspect it may be functioning correctly and it may be the boiler temperature cutout at fault. The reason for this thinking is that also intermittently, I can see the CH thermostat calling for boiler (digital therm with display), boiler comes on and lights but shuts down after a few seconds and the CH therm is still calling for the boiler. My thinking being if the boiler temp control is intermittently faulty to this degree at this end of the scale (heat exchanger not hot), it may also be intermittently failing at the other end of the scale and failing to shut the boiler down and hence the subsequent safety trip.
Any advice on testing this out or even wether parts are available or even capable of being replaced (corgi or otherwise) ? I'm not familiar with the mechanisms involved here as it is an area I've not been involved with before, but I'm guessing there is a thermocouple or similar involved here. Any advice or information welcome.

ChrisR · 3 Mar 2005

No thermocouple but the reset underneath is an overheat reset - is that the one you mean?

bathjobby · 3 Mar 2005

Yes thats the one Chris. I thought there would be a thermocouple or similar device controlling the boiler functioning temp and maybe that is at fault....

ChrisR · 3 Mar 2005

The predecessor, the Netaheat, didn't have a permanent pilot so I don't think any of the Neta Profs did, so no thermocouple.
It has a normal thermostat, which could be going awol and letting the thing get too hot, but that would take qhite a while. On a boiler that age it would probably make a bit of a racket if it were overheating.

By the way these are positive case pressure boilers which can be killers of the seal on the case is leaking at all - needs testing with corgi's kit. For info: http://www.partsarena.com/baxi

bathjobby · 3 Mar 2005

Thanks Chris.
Tiny bit of kettling occasionally thats all as I've tried to keep this system clean and treated. Sorry to be a pain but I'm trying to understand the thermostat mechanism and possibility of parts and replacement. You say a 'normal thermostat', could you elaborate and is it replaceable ?
Am also aware of the seal situation but had assumed these were negative pressure boilers (my term), i.e. after fan comes on, boiler won't ignite until there is a vacuum registered within the case.
Appreciate your time / trouble

namsag · 3 Mar 2005

There is a red switch on these that says pumped or gravity it should be set to correct position to stop boiler tripping out and i think original instructions used to say if used on gravity system don`t have boiler stat above 4

gasman24 · 3 Mar 2005

sounds like a dodgy overheat thermostat to me mate...
sometimes through age the contacts get weak and trip out intermittantly.
replace o/h stat

ChrisR · 4 Mar 2005

Positive Pressure. The case is pumped up with air from outside. Seemed like a good idea at the time - fan nice and cool, a leak not important, right?
Wrong. The fan sucks in a percentage of the products of combustion. If the case leaks, the combustion air % for the flame is altered, so it doesn't burn correctly, so it can produce some CO. SOme of that ends up in the room through the leak, and some goes back to the flame - which is upset further, so more CO is produced.
An ex BG inspector told us on a course of several dozen fatalities caused by faulty seals on Netaheats and Thorn Apollo's.

bathjobby · 4 Mar 2005

Thanks for all your replies, really appreciate it.

Gasman24, may well be but that wouldn't explain why sometimes the boiler shuts down after only about 5 seconds when the therm is still calling for the boiler ! This happens about as intermittently as the overheat trip going (not usually at the same time), which is why I was thinking boiler control therm 'getting tired' after 16 years maybe !

ChrisR, thats is scarry, can't imagine why they went positive instead of negative, apart from keeping the fan cool ! The link you gave is superb, thanks a lot.

cozzmic · 5 Mar 2005

If the boiler is set for grav HW the T/Stat probe needs to be fitted through the hole on the outer nut of the phile which goes into the boiler heat exchanger at the top right.

alanbaines76 · 6 Sep 2011

Sorry to be six years behind this post, but the issue exactly matches mine. The thermal trip keeps going after ~10 mins use, I have managed to get it working continuously by moving the trip thermostat to the outer position (in the nut head) so it is now not deep inside the heat exchanger.
Per the manual I have switched to gravity from fully pumped.

Just wanted some confirmation that this is OK - can I leave the thermostat sensor outside and continue in gravity and/or fully pumped modes ? Any comments appreciated

45yearsagasman · 6 Sep 2011

No its not OK. The red switch should be left as is appropriate for your system configuration. Moving the o/heat sensor is also a no no, as is doing all this inside the pressurised case when you have no idea as to all the dangers involved.

DeltaT2 · 6 Sep 2011

alanbaines76 said:
Sorry to be six years behind this post, but the issue exactly matches mine. The thermal trip keeps going after ~10 mins use, I have managed to get it working continuously by moving the trip thermostat to the outer position (in the nut head) so it is now not deep inside the heat exchanger.
Per the manual I have switched to gravity from fully pumped.

Just wanted some confirmation that this is OK - can I leave the thermostat sensor outside and continue in gravity and/or fully pumped modes ? Any comments appreciated

Oh my good Gawd, seriously mate; you need to get a Gas Safe RGI in to look at your boiler without delay!!!

bathjobby · 6 Sep 2011

Can't comment on your update alan but can update you on my situation. I Gave up and decided on a new boiler, hence will not know if some of the boiler components were dodgy or had been installed incorrectly. In addition to those symptoms, in the final days the boiler overheat trip would invariably go a few minutes after any call for heat had been completed. When they came to fit the new boiler they found that the boiler was wired up very basically i.e. when h/w or heating called for the boiler thats what it did and when temperature was reached i.e. calling stopped, thats exactly what it did and more importantly thats 'all' it did. It should have been wired up so that after the heating of the boiler chamber was stopped the pump should have continued to run for 10 mins or so to prevent the chamber overheating but it wasn't hence the chamber over heated and triggered the trip some minutes afterwards, which was a consistent final symptom.

Youllneverguess · 6 Sep 2011

alanbaines76 said:
Sorry to be six years behind this post, but the issue exactly matches mine. The thermal trip keeps going after ~10 mins use, I have managed to get it working continuously by moving the trip thermostat to the outer position (in the nut head) so it is now not deep inside the heat exchanger.
Per the manual I have switched to gravity from fully pumped.

Just wanted some confirmation that this is OK - can I leave the thermostat sensor outside and continue in gravity and/or fully pumped modes ? Any comments appreciated

Turn it off you obviously have no idea what you are doing.

Call a professional!

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Potterton Netaheat Profile boiler tripping

namsag

DeltaT2

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