High Limit button tripping on Warmflow Boiler thermostat.

[Pauli11]

I'm just asking out of interest, as I have a way of stopping this, but I am curious as to why it happens
When my Oil boiler thermostat on my warmflow boiler is set at about a bit under 4 everything functions fine. If I turn the thermostat up to 5, at some point it will trip the High Limit Button. I then stick a pin in to the button and the boiler restarts.

I read that 5 on the stat is around 89 deg? and the high limit button only cuts in about 110 deg? How would the boiler be reaching 110 deg to trip the button? The stat obviously functions because set at 4 there are no trips, set at 5 there are regular trips, but even at 5 the boiler should not get as hot as 110 deg. Am I reading this right, and what are the usual causes of the switch tripping?

 

[oilboffin]

It's a safety function I'd leave it if I was you if the boilers ok the flow is ment to be 75-80 c and that would give a return of around 50c which will be fine I'm a warranty engineer fior warmflow have been for years and that's how I set them with no probs. Check the circulating pump make sure it's getting rid of the water ok and leave well enough alone.Bob

 

[Pauli11]

Thanks. Yes I know the button is there for safety, but if its tripping when the thermostat is at anything higher than about 3.5 on the dial, I am querying why this happens?
As I originally posted, I read that the safety trip is at approx 110deg. If even the highest setting 5 on the stat is approx 89deg, why would it trip at a lower dial setting? I would have thought if all was working ok, it should even trip at 5?
I have knocked the thermostat off the boiler a few times while working round the garage (they aren't the best fitted things). I wonder could it be faulty?

Also if replacing, do I have to use the same one (below)? They are about £60. I have seen others about £29. Does the length of the dual probes matter?

 

[ianmcd]

I then stick a pin in to the button and the boiler restarts.

That is stupidity beyond belief, stop messing around with a safety device and get an engineer to look at it

 

[Pauli11]

That is stupidity beyond belief, stop messing around with a safety device and get an engineer to look at it

What are you talking about?? The red reset pin is there to reset the boiler if it trips out. It has only done that when the thermostat was up to 5, not when set lower. When at 3.5 it never trips. I am simply asking the question why it would trip at 5 and not 3.5

 

[oilboffin]

Some thermostats are more sensitive than others you could get another warm floe whose thermostat will only trip over mark 5.Bob

 

[oilhead]

With the thermostat set at 3.5, do the radiators get hot enough? The reason many boilers trip the limit is because the latent heat that builds after the boiler switches off exceeds the limit. A pump overrun stat can be fitted to negate this occurrence, but if 3.5 on the thermostat is hot enough, why bother?

 

[Red One]

With the thermostat set at 3.5, do the radiators get hot enough? The reason many boilers trip the limit is because the latent heat that builds after the boiler switches off exceeds the limit. A pump overrun stat can be fitted to negate this occurrence, but if 3.5 on the thermostat is hot enough, why bother?

Yes, the rads are hot at about 3.7 setting, but the stat trips at any setting over 4 (which obviously I never set it at) Over the last few years Ive replaced the 2 way valves, pump, expansion tank and had the system flushed and new inhibitor added.
The burner was serviced too. The only original thing remaining on the boiler is this Stat, so it might be worth changing out anyway.

 

[oilhead]

Yes, the rads are hot at about 3.7 setting,
So what is your problem? If it works satisfactorily why bother changing it?
If it's the only 'old' thing on the boiler, and you have money to throw away, then go ahead and change it. We don't know the output of the boiler or the demand of your system. If there is an imbalance, then you may have the same problem with a new stat.