External frost stat is in action or not doing anything?

[Jurgenjay]

Hi,

I have an external frost stat which I am not sure if it is in use or not. I had an electrician opened it and checked it, he said it is live. But he is not sure if it is in action or not....
I took a photo, could anyone confirm as the position it is, is this frost stat in action i.e. will protect boiler if temperature drops to some degree? If yes, what temperature it is set?

Thank you!

 

[John.g]

Measure or estimate the ambient temperature at the stat then just turn the dial slowly clockwise or anti clockwise until you hear a click, then note what reference mark, if any the temp setting on the dial that's closest to your measured temperature. (there seems to be a reference mark opposite 20C on the dial but very unlikely its set to this).
It should be set to 5C IMO.

Ensure boiler off before turning it up to check if boiler restarts, surprising the electrician didn't do this.

 

[Jurgenjay]

Measure or estimate the ambient temperature at the stat then just turn the dial slowly clockwise or anti clockwise until you hear a click, then note what reference mark, if any the temp setting on the dial that's closest to your measured temperature. (there seems to be a reference mark opposite 20C on the dial but very unlikely its set to this).
It should be set to 5C IMO.

Ensure boiler off before turning it up to check if boiler restarts, surprising the electrician didn't do this.

Thank you! Last night this Forum was down & could not open anymore....
Did you try to show me how to set the frost protection temperature? I am not sure about it.
Yes, I heard it should be set to 5C.
From the photo, are you able to see what temperature it is set to?

 

[John.g]

No, I can't really see from the photo where it's set to, its set to ~ 20C, if the REFERENCE MARK is where I am showing it with the arrow but as I said this is unlikely and why I suggest getting a household thermometer and measuring the (garage) ambient temperature close to the frost stat, then turn the dial clockwise/anticlockwise slowly until you hear a click, post a photo again when you hear/identify this.

 

[Jurgenjay]

No, I can't really see from the photo where it's set to, its set to ~ 20C, if the REFERENCE MARK is where I am showing it with the arrow but as I said this is unlikely and why I suggest getting a household thermometer and measuring the (garage) ambient temperature close to the frost stat, then turn the dial clockwise/anticlockwise slowly until you hear a click, post a photo again when you hear/identify this.

Hi John, Thank you again for your reply!

I just checked and turned the dial anti-clockwise, when I heard the click I stopped and took the photo(the green line & question mark is what you meant REFERENCE MARK, right?)---attached photo1;
The photo 2 is the garage temperature I just measured for where the boiler and frost stat locate;
The photo 3 is the original (without turning) position----At this position you cannot turn the dial clockwise anymore, it is to the end & stuck there----can only turn anti-clockwise.
As you can see from photo 1 and photo3, the REFERENCE MARK position is different now.

Also, when I heard the click---as per photo1 position, the boiler started to fire, burner light (green light) was on, and blue light was on, I went upstairs to see the zone valve for hot water opened & the pump made noise!

But I heard the external frost stat normally is wired to heating not hot water? Is my system correct?

Thanks!

 

[Gasmk1]

The arrow should be straight up the defence in the lager tooth sharp at top behind dial

 

[Jurgenjay]

The arrow should be straight up the defence in the lager tooth sharp at top behind dial

Thank you!
Did you mean the arrow (above"5") position should be straight up like attached photo? I marked a down-arrow on the wall, so is that the line should the arrow on the stat face up to?

 

[John.g]

The arrow should be straight up the defence in the lager tooth sharp at top behind dial

The 12 oclock position would seem normal all right.
The measured temperature is 12.5C and (photo1) so a setting of 8.5C which closed the contactsmeans that the stat has a offset (hysteresis) of 4C, if this is correct then the stat should be set at "2" or where it originally was which will close the contacts at approx 5C??.

 

[John.g]

Thank you!
Did you mean the arrow (above"5") position should be straight up like attached photo? I marked a down-arrow on the wall, so is that the line should the arrow on the stat face up to?

Yes, more or less correct, but a setting of 8.5C equals to your measured temperature of 12.5C so maybe repeat your test and if the same I would set the stat almost fully clockwise to its original setting of "2" which means that the stat will operate when the temperature is 5C?.

 

[Jurgenjay]

The 12 oclock position would seem normal all right.
The measured temperature is 12.5C and (photo1) so a setting of 8.5C which closed the contactsmeans that the stat has a offset (hysteresis) of 4C, if this is correct then the stat should be set at "2" or where it originally was which will close the contacts at approx 5C??.

The arrow straight up---if this means 5C then the original position(photo3) it means 0C?
My installer's boss who told me the installer(had left the boss) said"he had disconnected the external frost stat", if so, then the original position(0C?) means the frost stat is not in use?
Until today I turned the dial anti-clockwise and heard the click---which is photo1 position: the boiler started to fire, zone valve for hot water opened, green and blue light were on.
So at photo 1 position, the frost stat is in action? ---but today the garage is 12.5C which is too high for frost protection temperature?

 

[Jurgenjay]

Yes, more or less correct, but a setting of 8.5C equals to your measured temperature of 12.5C so maybe repeat your test and if the same I would set the stat almost fully clockwise to its original setting of "2" which means that the stat will operate when the temperature is 5C?.

Hi John, please see my earlier reply.
almost fully clockwise"2"---it might meant by the installer that "was disconnected"?

 

[John.g]

No, not at all, it just means that the stat will operate theoretically when the garage temperature falls to 2C that the stat will operate, you can't turn off a stat. but because the stat operated at a setting of 8.5C when the actual measured temperature is 12.5C then a setting of 5C will (probably) mean that the stat will operate at 9C which is too high,so suggest setting it to 2C which means it will operate at a higer temperature of around 5/6C.

To ensure that it's connected correctly you might turn off the HW and CH zones and carry out your test again, it should then fire up the boiler again.

 

[Jurgenjay]

No, not at all, it just means that the stat will operate theoretically when the garage temperature falls to 2C that the stat will operate, you can't turn off a stat. but because the stat operated at a setting of 8.5C when the actual measured temperature is 12.5C then a setting of 5C will (probably) mean that the stat will operate at 9C which is too high,so suggest setting it to 2C which means it will operate at a higer temperature of around 5/6C.

To ensure that it's connected correctly you might turn off the HW and CH zones and carry out your test again, it should then fire up the boiler again.

Thanks for letting me know the stat cannot be turned off! The installer(left the job) told his boss he disconnected the frost stat which now seems a lie to his boss (his boss does not know it is connected or disconnected hence I am asking here)

"the stat operated at a setting of 8.5C"---This is just the position when it clicked today, right? If so, everyday it could be at different position? As everyday temperature can be different? e.g. cold or warm days.

When the click happened, the boiler started to fire, the zone valve for hot water opened, green and blue light were on.
How do I turn off the zone valves for HW and CH?

 

[John.g]

""the stat operated at a setting of 8.5C"---This is just the position when it clicked today, right? If so, everyday it could be at different position? As everyday temperature can be different? e.g. cold or warm days.
It doesn't matter what the garage temperature is, if you have the stat set to operate at 5C then the garage temperature will have to fall to 5C before the boiler fires up, when the temperature reaches ~ 8/9C, the boiler will stop firing. You deliberately increased the setpoint to test the stat operation only.
"
You should or may have HW and CH selections on your programmer where you can set the times that you want them off and on, something like this one.

 

[Jurgenjay]

""the stat operated at a setting of 8.5C"---This is just the position when it clicked today, right? If so, everyday it could be at different position? As everyday temperature can be different? e.g. cold or warm days.
It doesn't matter what the garage temperature is, if you have the stat set to operate at 5C then the garage temperature will have to fall to 5C before the boiler fires up, when the temperature reaches ~ 8/9C, the boiler will stop firing. You deliberately increased the setpoint to test the stat operation only.
"
You should or may have HW and CH selections on your programmer where you can set the times that you want them off and on, something like this one.

On thread #5, photo 3 that is what the original position, you said that was set as 2C, right?

But you said suggest setting it to 2C which means it will operate at a higher temperature of around 5/6C.===why set it at 2C & will operate at a higher temperature of around 5/6C?
Why there's 4C difference?

I have the attached programmer, is this what you meant? I use this to set the timing for HW and CH start and finish time.

Thank you!

 

[John.g]

There is a difference of 4C because you discovered that yourself when the stat operated at a setting of 8.5C when the actual measured temperature was 12.5C , (12.5-8.5 = 4). All thermostats will have some difference between the setting temperature and the measured temperature, 4C might be a bit on the high side but you can compensate by making the setpoint 4C lower, in this case if you require the stat to operate at 5/6C you set it to 2C (6-4 = 2).

Re programmer, yes, that's it, so if you ensure both CH and HW Off then the boiler should still fire when you test it by increasing the frost stat setting until it clicks on. After testing, return it again to 2C.

 

[Jurgenjay]

There is a difference of 4C because you discovered that yourself when the stat operated at a setting of 8.5C when the actual measured temperature was 12.5C , (12.5-8.5 = 4). All thermostats will have some difference between the setting temperature and the measured temperature, 4C might be a bit on the high side but you can compensate by making the setpoint 4C lower, in this case if you require the stat to operate at 5/6C you set it to 2C (6-4 = 2).

Re programmer, yes, that's it, so if you ensure both CH and HW Off then the boiler should still fire when you test it by increasing the frost stat setting until it clicks on. After testing, return it again to 2C.

Yes, this afternoon I turned the dial anti-clockwise and when heard the click, I stopped, so the photo1 is the position as it was: 8.5C: the boiler started to fire, zone valve for hot water opened, green and blue light were on.
You mean to do this test again to obtain another setting temperature setting C or for what to do another test?
After testing, I turn it back to full clockwise i.e. 2C?

When you said setting frost stat at 2C, i.e. roughly the ambient temperature is 6C----this looks making sense for the case happened on 21st of January which the morning at 8:35am outside temperature was -6°C, and the garage (where my boiler is locates) temperature was 6.6°C, at the time, my boiler started to fire (outside of programmer setting period), zone valve for hot water opened, this lasted nearly 4 hours till 12:15pm.
So all this could be caused by the external frost stat triggered the boiler to start the frost protection function, right?

 

[John.g]

Don't think you need to repeat the test as the boiler fired up outside the programmed times so OK. The problem with this type of frost stat is that it is measuring a "room" temperature, ie the garage which is only heated by any radiated heat loss from the boiler so takes hours to reach the frost stat cut out temp which can be 4 to 6C higher than its setpoint.
If you were/are quite happy with the boiler itself which monitors the water temperatures and will only fire for the very minimum time required to prevent the water freezing, then all that probably has to be done to disable the external frost stat is to remove one wire in the stat.

You had another thread where it showed the parameters for the internal frost protection which seemed perfect.

I would suggest getting back on to the "boss" and tell him that the external stat is not disconnected.

 

[John.g]

You said.....
Below is the manual of my boiler regarding Frost Protection：

"If the temperature within the boiler falls below 8°C the pump will run to circulate water and prevent the system freezing. If the temperature within the boiler falls below 5°C the boiler will fire periodically, bringing the boiler temperature up to 12°C to avoid the possibility of the system freezing. This process will be repeated until such time that the boiler temperature does not drop below 5°C."

This is the full explanation of the above.

If the temperature within the appliance falls below 8°C the pump will run to circulate water and prevent the system freezing. – If the temperature does not rise to 9°C within 30 minutes of the pump operating, the appliance will fire up. ▶ If the temperature within the appliance falls below 5°C the appliance will fire immediately, bringing the appliance temperature up to 12°C to avoid the possibility of the appliance freezing. ▶ This process will be repeated until such time that the appliance temperature does not drop below 8°C."

 

[Jurgenjay]

Don't think you need to repeat the test as the boiler fired up outside the programmed times so OK. The problem with this type of frost stat is that it is measuring a "room" temperature, ie the garage which is only heated by any radiated heat loss from the boiler so takes hours to reach the frost stat cut out temp which can be 4 to 6C higher than its setpoint.
If you were/are quite happy with the boiler itself which monitors the water temperatures and will only fire for the very minimum time required to prevent the water freezing, then all that probably has to be done to disable the external frost stat is to remove one wire in the stat.

You had another thread where it showed the parameters for the internal frost protection which seemed perfect.

I would suggest getting back on to the "boss" and tell him that the external stat is not disconnected.

Hi John,
Thank you so much for your input throughout this thread! I got more useful information from you---on this website forum!
I should got all those answers from the gas engineer boss/team as they installed the boiler and all system, but the boss did not know the boiler/built-in frost protection/external frost stat/ zone valves how they work/should work etc. which forced me had to ask online! What a sad thing.....

As you suggested, I may need to get the external frost stat disconnected as it may conflict with the built-in frost protection?
I don't know how other houses do when they install a new boiler system i.e. get rid of the old external frost stat as nowadays new boiler normally has built-in frost protection already?