Boiler firing - frost protection question

[mpearcey]

HI,

We've got a Danesmoor 20/25 oil boiler - looks like its got a frost protection stat attached which is overriding our main controller (hive) and causing the boiler to fire when not wanted.

The frost stat is a Sunvic TLM2257, but the weird bit is that it's installed outside, in an IP56 rated box, on the wall. This makes no sense to me as I'd expect the frost protection stat to be installed indoors.

Would welcome any views as to why this was done before I disconnect it...

Cheers
Matt

 

[oldbutnotdead]

Depends what the frost stat is protecting. If the boiler is in an unheated room or you've got uninsulated pipe runs going through cold spaces then outside temperature is a useful parameter

 

[stem]

Usually the person who installs a frost stat surveys the installation and selects the best place for it. There are no hard and fast rules as every property will be different.

Usually where pipes / tanks / boiler are in an unheated garage / outbuilding / roof space, the frost thermostat is located in there. However, if there are several areas at risk, there may not be one position that could provide the required frost protection for all of them.

Occasionally I have seen frost stats located outside, although they were on larger non domestic buildings, or where some pipes were physically outside where they run between buildings for example. When located outside you maybe able to set it a few degrees lower than one located inside. OC as opposed to +5C, and still achieve the required protection.

However, even when it's on, there should be a pipestat on the return pipe to the boiler that switches it off when the return pipe reaches about 10C, which wouldn't even feel warm to the touch, meaning that the boiler shouldn't be running for very long.

If you want to disconnect I would make sure that by doing so I wasn't putting any part of the system at risk of freezing. I guess there would have been a reason for it being there in the first place.

 

[mpearcey]

thanks folks.. the boiler is inside the house, all pipe runs are inside the house, and as far as I can tell there is no pipe stat anywhere in the system unless its deeply hidden somewhere... but I'm assuming it should be near the boiler on the CH return, and there is nothing that I can see... which I presume is causing the system to run continuously (or at least until the external stat hits the target, which will have nothing to do with the boiler running).

 

[stem]

Here's a Pic of a pipe stat on the boiler return from a post earlier this week. The frost stat is indoors here though.

 

[mpearcey]

Here's a Pic of a pipe stat on the boiler return from a post earlier this week. The frost stat is indoors here though.

View attachment 289203

Cool - thanks... no evidence of a pipe stat at all in the system... which would explain the continuous firing of the boiler when the externally mounted frost stat kicks in. I've confirmed there are no external pipe runs, so I've disconnected the external stat & will let the Hive system's frost protection take over (although as the wife has flu, I'm not going to drop the temp to 7 to test it right now...)... everything else is behaving right now...

 

[oldbutnotdead]

If the boiler is in an unheated room that might be a risky strategy at the moment- due to the persistence and depth of this frost I've got one burst pipe to deal with already (that has not frozen in the last 10 years).

EDIT Pipe stat on the boiler return in series with that external frost stat would work fine- wired so boiler fires if external frost is true and return pipe < 10°.

 

[mpearcey]

If the boiler is in an unheated room that might be a risky strategy at the moment- due to the persistence and depth of this frost I've got one burst pipe to deal with already (that has not frozen in the last 10 years).

EDIT Pipe stat on the boiler return in series with that external frost stat would work fine- wired so boiler fires if external frost is true and return pipe < 10°.

This is the weird thing - its not in an unheated room - its a boot room next to the kitchen, where we have an Aga that is always on, so pretty much the warmest room in the house - plus there is no pipe stat at all, hence the boiler firing but not turning off until the outside temp triggers the frost stat to switch off - its like someone forgot to put the pipe stat into the system (if that was what they were aiming for).

 

[stem]

I know of one frost stat that was installed for someone who left their house unoccupied for long periods of time during the winter whilst they went to sunny climes. Like you they didn't have any plumbing that would normally be considered 'at risk' But because the property was empty and the heating not on, the whole installation was at risk. It was wired up so that they could set the internal room thermostat to 10C before they left, but the heating wouldn't come on at all unless the frost stat in an external garage (so effectively outside) dropped to 0C. It the frost stat did switch on the house was only heated to 10C.

That is unusual way of installing one though. Normally frost stats are wired to work independently from the room stat, and come as a kit with a pipe stat.