Frost Stat Queries

[Rautospoon]

I had a Vaillant ecoTech Plus Open Vent boiler fitted in my loft about 6 months together with replacement Honeywell Frost (set at 3C) and Pipe (set at 20C) stats.
These replaced a 30 year old boiler (Ideal Classic NF40) and identical frost and pipe stats, again in the loft to my bungalow.
My queries are :
1. What could be considered a "normal" time period between the boiler "kicking in" (when the air temperature falls to 3C) and it stopping (when the temperature in the return pipe reaches 20C) and vica versa ?
2. Does the frost stat temperature (3C) or the pipe stat temperature (20C) have priority ?
3. If the CH is "on" and has reached temperature on my Drayton room stat and has turned off, will the boiler still "kick in" if the temperature in the loft falls to 3C ?

I ask as the new boiler seems to come "on and off" more (in the current cold weather) than my previous one.
Many thanks.

 

[Stuckinarut]

All could have varying answers. Are pipes insulated and were they previously? The frost stat and pipe stat should be wired in series (afaik) and will override any other controls. How long would be dependant on how much time it takes to heat up to the required temperature.

 

[Rautospoon]

The pipework in the loft is now well insulated, better than before.
The frost stat are wired in series, does one override the other ?

 

[JayN]

I recently rewired my frost and pipe stats in my cold garage, and tested them by switching off the boiler so the pipes in the garage got cold, then turned the frost stat dial and had the pipe stat set to 20-30degrees IIRC. There was a long lag, pipes got really toasty before the pipe stat switched off the boiler. I was getting worried but in the end, boiler shut off.

 

[stem]

The frost stat are wired in series, does one override the other ?

Because they are wired in series, both thermostats have to be calling for heat at the same time to trigger the boiler. So, as yours is currently configured, it must be 3 degrees or lower where the frost stat is located, and also 20 degrees or lower at the point the pipe stat is sensing.

Once the temperature where either the frost stat is located gets above 3 degrees, or the pipe stat gets above 20 degrees the frost protection is switched off.

 

[Rautospoon]

Can anyone provide any additional information in reklation to my 3 queries ?

Because they are wired in series, both thermostats have to be calling for heat at the same time to trigger the boiler. So, as yours is currently configured, it must be 3 degrees or lower where the frost stat is located, and also 20 degrees or lower at the point the pipe stat is sensing.

Once the temperature where either the frost stat is located gets above 3 degrees, or the pipe stat gets above 20 degrees the frost protection is switched off.

Many thanks for the detailed response. appreciated.

 

[Rautospoon]

Please forgive my ignorance, but as the pipework around my boiler is well insulated why are a frost and pipe stat actually needed ?
Is it for any other reason than just "insurance" ?

 

[ChrisJP]

If there's no source of heat in the loft then, even with the best insulated pipes, they'll eventually get down to the outside air temperature. Insulation can't create heat, it can only retain existing heat for a certain time period

 

[Rautospoon]

If there's no source of heat in the loft then, even with the best insulated pipes, they'll eventually get down to the outside air temperature. Insulation can't create heat, it can only retain existing heat for a certain time period

Thanks for that, which makes perfect sense but how about the (well insulated) pipework connected to the CW and F&E tanks in a loft - why are we not generally concerned about these freezing ?

 

[ChrisJP]

If the house is unoccupied and has no heat on, then there is a very real chance that the CW storage tank and F&E tank pipes in the loft will freeze.
This can be averted for the F&E by putting combined inhibitor and anti freeze into the central heating system.
For the CW and indeed HW system it's usually the advice to drain these down if you plan to leave the house unheated in the Winter.

 

[Rautospoon]

The point I am (unsuccessfully !) trying to make is why (in normal operating situation) boilers (in lofts) with well insulated pipework are protected by frost stats whereas (insulated) tanks with well insulted pipework are not. ?
I am not taking in any way about the situatuon where a property is unheated and/or unoccupied.

 

[ChrisJP]

Good point!
However, I'd always assumed that frost stats on CH boilers were there solely turn on the boiler when there are freezing outside temps and thus keep all water systems in the house from freezing up, but only when it was unoccupied in Winter
I have never thought that frost stats have any role when the house is occupied and heated.

 

[oilhead]

What we don't know, and maybe ,neither do you, is how the last boiler was wired.
For the frost stat on the return to reach 20c, then the rest of the system will be at or above that temperature (all through the house). Many of my customers did not want, or need that levle of protection, and I have modified boilers in garages so the the pipe stat is at the exit of the flow pipe into the house. This protects the boiler and pipework, even to some extent the return as it invariably follows the same path as the flow. If protection is required for the main system, this can be achieved by running the boiler on constant with the room stat set to 10C or so.

 

[Rautospoon]

The original boiler was wired in identical fashion to the current one viz. "in series" with the pipe stat on the return pipe in the identical position as previously.
I am only concerned about "frost protection" in the loft to my bungalow.
My bungalow was a "new build" 31 years on an estate of approximately 100 homes, half approximately of which (those with the boiler fitted in the integrated or attached garages) had frost stats fitted as standard. My bungalow had an integrated garage (with boiler) that I subsequently converted moving the boiler up to the loft.