Frost Protection of Heating System

[DIYWell]

I'm planning to leave a house unoccupied over the winter and popping round to check on it is not an option thanks to the distance. Hot water is supplied on demand from the boiler, so that's not a worry. Mains water I'll turn off at the stop cock and leave taps open to allow for expansion so I'm happy with that.

Heating system is another matter. One option is to drain the heating system, but I've raised that in a previous thread. Another option is to leave the heating running but that's just expensive/wasteful, even tuned down low. Final option is fitting some sort of frost protection circuitry which is where I could use your help.

In another, more local, property I manage which has a heat only conventional boiler, it's fitted with an external frost stat which kicks in at an unknown temperature, and a pipe stat to shut it off when the return hits around 10C. This appears to work.

Boiler in the abandoned house is a 2 year old Viessman Vitrodens 100-W combi controlled by a wireless controller beyond my comprehension, but it works to heat the house, not protect the pipework. It has a boiler frost protection function (too cold, fires up, heats itself, doesn't run the pump, shuts off).

My current thoughts are to wire in a frost/pipe stat pair to the terminals where an old school room thermostat can be connected akin to the system I'm familiar with. However, frost stats I found with a quick search are internal rather than external. So, if I were to fit a Drayton RTS3 in the coldest part of the house, do I need to think differently about what temperature to set it? Would I still set it to kick in when the air temperature drops below 5C and the pipe stat below 10C? I think yes, since the pipework can't be cooler than air temperature.

Your thoughts please.

 

[oldbutnotdead]

You need to risk-assess the whole situation. You may find that your insurance is invalid if someone doesn't drop in every 4 weeks or so. If its an older house (thinking solid walls, limited insulation) you may get problems with damp and mould if you leave it unheated for prolonged periods (even assuming the temperature stays above freezing).
It might be worth the £200 or so to upgrade the controls to internet-capable (so yes you'd need some broadband- cheapest is probably a budget smartphone with a PAYG SIM card on one of the many cheap offers round at the moment, massive bandwidth not required)- this would give you a system with a setback temperature setting (mine is set so if internal temp drops below 12 degrees the heating comes on whatever time of day it is), you can check the house temperature from wherever you happen to be, you can remotely fire an hours boost if there's a cold snap.....
Make sure the system is full of inhibitor (that depresses freezing point), chat up the neighbours, see if you can find someone who has the time to drop in every day or 2 to clear junk mail and check for squatters as well as water leaks.

 

[stem]

I remember as a teenager accompanying my plumber father to a property that had been left empty for the winter (the original owner was in prison I think) the water had been drained as far as possible, but the new occupier discovered several burst pipes when he refilled it, because the pipes couldn't be emptied completely, and there were sections below the floor and in the loft that still had some water in. Enough to freeze and split the pipes. I can't remember how many there were but it took a whole day to find and fix them all.

So maybe frost protection is a better alternative. Although, winters seemed worse though when I was a lad (late 1970's)

 

[fixitflav]

Boiler in the abandoned house is a 2 year old Viessman Vitrodens 100-W combi controlled by a wireless controller beyond my comprehension, but it works to heat the house, not protect the pipework. It has a boiler frost protection function (too cold, fires up, heats itself, doesn't run the pump, shuts off).

Assuming there is a roomstat, I would set it at 10°C and leave the system on 24/7. That won't cost a fortune and IMO worth it for the peace of mind.

 

[polesapart]

Although, winters seemed worse though when I was a lad (late 1970's)

Aye, you're right there, lad.

I remember the milk bottles freezing on the doorstep in 62/63 and the iced cream slush pushing up the foil caps.
And this in suburban London!

I'm surprised no-one else has noticed, commented upon or indeed protested about this phenomenon.

 

[fixitflav]

the milk bottles freezing on the doorstep

That happened several years in the 60s, and of course 62/63 was particularly bad. But there were some good frosts in late 70s, my ex-late father-in-law had a 45 gallon drum as a water butt, which froze solid.

 

[Harry Bloomfield]

I remember the milk bottles freezing on the doorstep in 62/63 and the iced cream slush pushing up the foil caps.
And this in suburban London!

I'm surprised no-one else has noticed, commented upon or indeed protested about this phenomenon.

Several years before that, I remember having to shovel snow, just to get out of the front door, and trains becoming stuck in the snow.

 

[DIYWell]

You need to risk-assess the whole situation. You may find that your insurance is invalid if someone doesn't drop in every 4 weeks or so. If its an older house (thinking solid walls, limited insulation) you may get problems with damp and mould if you leave it unheated for prolonged periods (even assuming the temperature stays above freezing).
It might be worth the £200 or so to upgrade the controls to internet-capable (so yes you'd need some broadband- cheapest is probably a budget smartphone with a PAYG SIM card on one of the many cheap offers round at the moment, massive bandwidth not required)- this would give you a system with a setback temperature setting (mine is set so if internal temp drops below 12 degrees the heating comes on whatever time of day it is), you can check the house temperature from wherever you happen to be, you can remotely fire an hours boost if there's a cold snap.....
Make sure the system is full of inhibitor (that depresses freezing point), chat up the neighbours, see if you can find someone who has the time to drop in every day or 2 to clear junk mail and check for squatters as well as water leaks.

Insurance was selected so there isn't a regular inspection clause but they require 12C or drain down. Insurers have no concept of weather compensation or frost stats. Current controller can do a 12C setback, and when I did that for 21/22, keeping the house at 12C for 5 months cost £2k5. Prices have risen, so not worth keeping the heating going.
Good point about adding more inhibitor though.

 

[DIYWell]

Ok, so essentially I can replace the frost stat with a room stat so long as I can turn it down low enough. So, room stat down to 5C, pipe stat set to 10C. Room stat will make a demand for heat if the air temp is lower than 5C, pipe stat will shut the boiler down when the return pipe hits 10C.

 

[fixitflav]

Ok, so essentially I can replace the frost stat with a room stat so long as I can turn it down low enough. So, room stat down to 5C, pipe stat set to 10C. Room stat will make a demand for heat if the air temp is lower than 5C, pipe stat will shut the boiler down when the return pipe hits 10C.

Why replace the frost stat with a roomstat? Don't you have a roomstat? That would be unusual.
Maybe 10C for the roomstat is a bit generous, but need to account for any corners of the house which can get colder than the roomstat location.

 

[DIYWell]

Why replace the frost stat with a roomstat? Don't you have a roomstat? That would be unusual.
Maybe 10C for the roomstat is a bit generous, but need to account for any corners of the house which can get colder than the roomstat location.

The wireless controller is a roomstat, but it is essentially an always on device calling for heat according to programmed temperatures. But I'm not trying to control the temperature of the house, just the pipework.

Using an old fashioned bimetallic style room stat means there's an on and an off to pair with the pipe stat wired in series. Room stat cuts in at 5C, pipe stat ensures it cuts out when the pipe comes to temperature.

If flow is set at 55C, return should be 35C if the system were heating the house. If I set the pipe stat to 20C, then enough heat flows through the pipes to prevent freezing, but not enough to warm the air much. During cold spells, the hysteresis of the pipe stat does the work.

 

[Harry Bloomfield]

If flow is set at 55C, return should be 35C if the system were heating the house. If I set the pipe stat to 20C, then enough heat flows through the pipes to prevent freezing, but not enough to warm the air much. During cold spells, the hysteresis of the pipe stat does the work.

Are you locating the pipe stat on the return, close to the boiler, so the entire system is warmed, before it shuts down?

If so, you could maybe set its temperature a bit lower than 20C

 

[DIYWell]

Are you locating the pipe stat on the return, close to the boiler, so the entire system is warmed, before it shuts down?

Yep, on the return

 

[DIYWell]

so, you could maybe set its temperature a bit lower than 20C

Yer, been thinking about that. Pipe stat has a 5 degree hysteresis. If I set it to 10C, during cold snaps, I'm probably keeping the flow toastie but the return won't drop below 5.

As it's effectively the pipe stat that's doing the controlling, I'm not really changing the frequency of the cycling that much as it's really down to how quickly the pipe cools.

 

[oldbutnotdead]

Insurance was selected so there isn't a regular inspection clause but they require 12C or drain down. Insurers have no concept of weather compensation or frost stats. Current controller can do a 12C setback, and when I did that for 21/22, keeping the house at 12C for 5 months cost £2k5. Prices have risen, so not worth keeping the heating going.
Good point about adding more inhibitor though.

That must either be a mansion or have no insulation, no double glazing, no carpets or maybe its on the top of a hill in Scotland?
My worst heating days last winter (so 22-23) were £5 a day to keep a 4 bed at 19 deg, part insulated and part not...