overheat trips out boiler & pilot goes out

[gazkazdiy]

Boiler (Yes its old) New World CH502
Natural gas
Thermo couple (with interupter)

Problem - once the hot water gets up to temperature, the overheat button clicks out, main burner and pilot goes out.

When left for a little while, if the overheat button is then reset, the pilot can be manually lit (and stays lit), if the boiler is then run (the water is of course already pretty hot) the main burners run for a short while and then above problem repeats.

As pilot remains lit intially-assume thermocouple ok.
Pump runs OK.
Pilot burn clean, no change in flame of late, flame touching top 25% of thermocouple.

Assumption (amateur)

- faulty thermostat is not turning off main burners when water temperature setting reached - causing overheat.

- faulty overheat switch, triggering in error.

- Gas valve faulty not being switched off by thermostat causing overheat.

Questions
1)In laymans terms, is it possible to do DIY tests to acertain which of above may be the problem ?
2)Any other likely causes ?

Thanks in advance for the help.

Regards Graham

 

[oakland99]

poss faulty thermostat, poss faulty overheat, poss faulty thermocouple, less likely gas valve, either way you need a corgi guy to look at it but brace yourself for the answer you don't want,,,new boiler.

 

[gazkazdiy]

I like to have the answer to the problem first,
- although that would would not be a problem with a genuine CORGI guy
- however a good bullsh**ter is hard to spot (& expensive if I don't check it out first). Cheers.
DIY help to identify cause would be helpful.

 

[WDIK]

look at your pump

 

[gas4you]

I would look at boiler stat first, but with something this old there may be no spares available

 

[namsag]

Boiler stat but most likely but to check gas valve turn boiler on and then turn stat down (do this several times to confirm) and make sure burner goes off and just leaves pilot and not even a peep of gas light on main burners.
No chance of spares IF stat , doing well to still be going the 502 and its predecessor the 501 now getting on for 38 year old.

 

[gazkazdiy]

Pump fine, as above.

Fired her up, bless her (about 38 would be about right, only 12 behind me; and she's only cost 2 thermocouples in 19 yrs & £55PM nowadays- for water & central heating- 3 bed house). Will miss her.

Turned thermostat fully clockwise to nil & back to halfway several times - main jets just continued full bore & unabated.

I would have concluded it down to stat not tripping out gas valve or gas valve not closing, your post would indicate it as more definitely the latter, would that be a fair assessment.

Advice very much appreciated.

(NB -Been looing at an Ideal HE18 classic for a while just in case it went "no spares/uneconomic", any thoughts - seems about as efficient and technologically minimalist as I can find, may not be as efficient as some or even their icos version but then less to go wrong and a lot less parts/IT than a combi etc. UK based in Hull, long established Co, spares etc, and as far as I can tell based on a prety bullet proof predesessor).

Best wishes and regards, Graham

 

[namsag]

Ideal classic is a really reliable boiler and one of the best out there but buy it as a OPTIA from plumbcentre it is exact same boiler with a different badge but at £424 plus vat and flue set.

When you open side door of your 502 what does the gas valve look like. does it have a knob that turns from off to pilot to main gas or is it a grey push button.
To double check gas valve with it firing turn power off to boiler does main burner go straight out or carry on firing .
If it goes straight out its the stat thats faulty if it carries on firing its the gas valve

 

[robbo9002]

If you are looking to replace it bud wouldn't think of touching an Ideal, yes they are a British company but I'm afraid that in current boiler terms they are way behind the likes of Worchester and Valliant.
Personally I only fit either of these two brands, they are reliable and if you do have any probs both have excellant technical help.You will pay more for either of these compared toa Ideal but you do get what you pay for.
Both of these brands are very reliable and I work within the trade as a technician.

 

[namsag]

So if you work within the trade you will know the classic has been just about the most reliable boiler out there for the past 15 years and still going strong .
Recent Ideals are sh#te but not the classic

 

[robbo9002]

Yes I do know the classic is a reliable and basic appliance, but it also does not confirm to the current efficiency regs i.e. condensing boilers with the odd exception. Why fit a less efficient appliance if not req????

P.S. worked on hundreds of classics and yes they are reliable, but so are Baxi 401s but again current legislation doesn't allow us to fit them.

 

[namsag]

Eh yes it does the classic and optia HE is band B which meets the regs,

 

[robbo9002]

But why fit a band B when you could install a band A?, which we all know is where the regs will be in a couple of years.
IMO I would go for a Worchester condensing appliance either system or combi whatever your req is, will cost more to install but will save in the long run.
But that is only my humble opinion

 

[namsag]

We all have our favourites rob and nothing up with that but as a customer i would be looking not only what would save me money on fuel cost but also on actual running costs over say a 15 year period.
Personall opinion based on how good the classic has been this will beat any vaillant or worcester hands down over this period.

 

[gazkazdiy]

Hi namsag

Many thanks again.

First option. knob goes from off, to pilot, to main.

If I switch the power rocker switch off whilst main burner lit, goes straight off, from your excellent advice I would take it that its the stat (install book calls it a modulator)

-gather from your earlier post, if it's the stat its new boiler time.

Thanks namsag for the opinion on the ideal too, plus the cheaper rebadge version. Yellow pages out tomorrow I think & off to nearest plumbcentre.

Thanks for your opinion too Robbo, I'm sure valiant and worster are also way ahead of my New world CH502, but likely to last 38yrs and cost 2 thermocouples in 19yrs ? with no tech advice needed till now. I'm afraid I would fit another tomorrow if I could get a new one (& £55 pm is the cheapest gas bill against my neighbours & mates ). But even the ideal has one fan and one circuit board more than i would prefer.

Combi's seem most hi tech - but I have been advised most will see 5 years out and a worster maybe 10 or so. Sorry Robbo but it's low tech and simple for me, I may regret it and will honestly let you know if I do.

Genuine and sincere thanks, for such real, practical and quick advice.

Regards Graham