High Temp Thermostat keeps tripping

marcoslupo · 25 Jan 2006

Hi..
I have a Glow Worm Xtrafsat 96 (Saunier Duval) and the High Temperature Thermostat keeps tripping. I recently had quite a clogged up system so I drained the system, added a cleanser, ran it for 4 weeks and the drained it out again. I then added some 'preserver' upon refill and since then every couple of days the HTT just trips leaving me with no hot water or heating (the boiler just humms [water pump] but won't 'let itself' ignite). I then remove the cover to the combustion chamber and press the reset 'nipple' on the sensor with the tip of a screwdriver. It's then OK again for a day or so.
Couple of notes that may help diagnose this:
The boiler itself (when the heating is working) is on nearly 100% of the time. I've got 11 rads, but I feel the boiler shouldn't have to work that hard (and I'm sure my gas bill is growing!).
I've replaced the HTT so as to elimnate the possibility of a faulty part. Alas, it still keeps cutting out.
Can anyone help? The plumbers I have called seem to have less of an idea than me!
Many thanks in advance.

fitz1 · 25 Jan 2006

not sure about this boiler but u may have clogged some internal filters.maybe one of the other guys knows this boiler.

fitz1 · 25 Jan 2006

is it a combi

marcoslupo · 25 Jan 2006

Yup, combi indeed.
http://www.tradecounter.com/dbdocs/glowwormxtrafast96-120fannedflueuserguide.pdf_tcc_01-04-04.pdf
Thankyou..

fitz1 · 25 Jan 2006

what code shows

ACOperson · 25 Jan 2006

Pump turning?

Air in system?

Could also be the overheat stat itself, once operated a few times (10-20) they become more sensitive than they should be and need to be replaced.

marcoslupo · 25 Jan 2006

Thanks for speedy response.
Fitz - The display reads a fault code:
05 - overheating

And thanks too ACO, but I've already replaced the Thermostat. Still behaves exactly the same.
Pump seems to be getting water round the system fairly well.....
I'm starting to think that this system is full of bits, as I can hear alot of 'tinkling' sounds rushing through the boiler intermitantly. Do you people think getting a company to come round and flush the whole system out (incl. boiler) is a good idea?

ACOperson · 25 Jan 2006

If the boiler is very badly scaled up and the scale is retaining the heat and causing the o/h stat to trip then a powerflush alone may not sure this. You may also need to descale the heat exchanger(s) in the boiler. To do this you need to close the boiler off from the rest of the CH circuit, add the neccessary chemicals and run it to a certain temperature. the combination of the chemicals and the heat can shift the layers of crud from the h/e and it will not trip out any more. Its a complicated procedure though, if its needed its best left to a professional who has done it many times before.

Softus · 25 Jan 2006

My t'penn'orth:

marcoslupo said:
And thanks too ACO, but I've already replaced the Thermostat. Still behaves exactly the same.

Remember - this doesn't necessarily mean that you don't have a faulty HTT.

marcoslupo said:
Pump seems to be getting water round the system fairly well.....
I'm starting to think that this system is full of bits, as I can hear alot of 'tinkling' sounds rushing through the boiler intermitantly. Do you people think getting a company to come round and flush the whole system out (incl. boiler) is a good idea?

If you have a sludged or scaled heat exchanger, then it could be the cause of your problems, but if the boiler is having to keep lit until the HTT trips, then your room stat is not switching off; or do you not have a room stat?

Also, regarding the pump, it's not clear what you mean by "fairly well.....". It's possible that the pump is worn and not circulating adequately - do the rads get too hot to hold? All of them?

ACOperson · 25 Jan 2006

Softus,

Could it not be a combination of pump not moving heat around quickly enough & heat excahnger overheating due to scale deposits retaining too much heat?

The plot thickens...

Softus · 25 Jan 2006

ACOperson said:
Could it not be a combination of pump not moving heat around quickly enough & heat excahnger overheating due to scale deposits retaining too much heat?

I see no reason why that could not be the explanation.

I still suspect the pump first though - the tinkly sounds could be kettling resulting from poor flow rate.

marcoslupo · 25 Jan 2006

Hi again..
Had the heat exchanger off a few times now as the 1st problem I had (about 4 months ago) it came up with fault code 9.....which turned out to be the Heat Exchanger being quite badly blocked with scale. Have checked again and the 'domestic' side of the HE is a black colour, but not full of scale. Water seems to run through it OK when I've fired a garden hose through it!
With all of your advice, I think I'm gona have to flush it AGAIN and check what comes out. Might try to get some mains pressure through the rads at the bottom of the house as they seem to not get quite as hot as rads on floors 1 & 2.
Do you guys/girls agree that if it doesn't get any better or cure the problem.......I may have to splash out and try a new pump?
Seems like I've already spent half of 2006 in my boiler cupboard! Rather be having a pint, but there you go.
Does anybody fancy a visit to check it out? I'm in Norfolk and make really nice tea/coffee!

ChrisR · 25 Jan 2006

Take the pump out, check it isn't blocked. SOmetimes the impellers fill with goo so you just get a spinning disc doing b all.
Tinkling is usually air or corrosion -derived gas.

ACOperson · 26 Jan 2006

Sorry am in London mate.

Softus · 26 Jan 2006

ACOperson said:
Sorry am in London mate.

Someone has to be

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High Temp Thermostat keeps tripping

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