Frost Protection for Heating system

[robbie98]

Hi Guys,

I have just found your forum and wonder if you can help me. I have an oil fired system which only has a manual switch on the wall, no timer, no stat, no TVRs, nothing.

What I want to do is install some form of timer device to switch on as required and also a frost stat to ensure it comes on when it gets really cold.

I have previously installed these components on gas heated systems but never worked on oil systems before. So I am comfortable in working on the units

My main question (I am sure there will be more after of course ) is whether the current requirements of the oil boiler is too high to simply fit the timer units. Do I need the timer unit to operate a form of relay or larger switch to operate it??

The main on/off switch currently looks like an old two pole switch but this could just be what the used at the time of install I dont know, so could be a red herring. The size if the switch is what is making ask about the current rating.

I guess another way of looking at the issue is what would the max switching current be for the timer units and stats??

 

[gas4you]

As far as I know the only difference between a domestic oil and gas boiler in terms of power demand is that the oil boiler is usually fused at 5 amps as opposed to gas at 3 amps.

All ch controls are designed for this purpose so no relays or contacters etc will be needed.

The frost stat should be wired in series with a pipe stat, fitted on the boiler return, so when the air temp drops the boiler won't fire until the water temp in the return pipe gets too low also.

Without this the boiler will probably fire all night every night in winter

 

[robbie98]

Thanks Dave and a good idea about the frost stat being in series with the pipe stat too, makes good sense.

I also assume the frost stat is in parallel with the normal stat if there are two of them. If not, would this be fine as the boiler is in the back part of the house which is probably the coldest part of the building but not where I would want to monitor during the summer months.

With regard to the timer, am I right in saying it will control/interrupt the live feed for the boiler to take control?

The boiler is in France and I haven't checked if there is a panel where I can fit a control lead from the timer unit. I am really after something which will switch the physical live for the boiler, unless I am barking up the wrong tree......

 

[wilhelm]

with ref to this

looking at the wiring diagram on page 2, just wire in the low range pipestat , there is no need for frost stat. so wire perm live to 1 on pipestat, so it sends poewer to m.v. etc

the only issue with programmer is to ensure the live for the burner operation does actually go through/via the limit stat, and hence through the boiler stat, easily checked after fit, because your control stat will /should turn burner off with prog on.

 

[robbie98]

thanks guys, it all makes sense now

 

[robbie98]

one extra thing to note here is that Honeywell make 2 different pipe stats, one os for 10-40 degrees and the other 50-95 degrees.

Of course for the frost stat, you will need the cooler 10-40 degree unit

 

[AlanE]

with ref to this

looking at the wiring diagram on page 2, just wire in the low range pipestat , there is no need for frost stat. so wire perm live to 1 on pipestat, so it sends poewer to m.v. etc

Leaving out the wall mounted frost stat and just relying on apipe stat will mean that even when there is no frost, but the water in the pipe is cold the boiler will cycle on and off just keeping the pipe temp around 5 degrees.

A total waste of fuel!!

 

[ChrisR]

I would have thought it worth keeping the pipe at 5 degrees, Alan?


ANother point though if you miss out the atmospheric stat, is that the place you've put the pipe stat might not be the coolest, due to wind chill or whatever.
If you use an air stat at say 5 degrees, and a pipe statt at 10, you know that all the pipe throughout the system must be warmed.
If things justify it, you sometimes have to make sure the pump's on, to prevent cold-spots developing.

These stats are not wired simply across the existng stat, they have to bypass any timers too.

 

[wilhelm]

Leaving out the wall mounted frost stat and just relying on apipe stat will mean that even when there is no frost, but the water in the pipe is cold the boiler will cycle on and off just keeping the pipe temp around 5 degrees.

A total waste of fuel!!

think about what youve just said.........

if its down to 5*c , 41f...........then i think you need the boiler ON..

you clown.

 

[robbie98]

also I am going to connect a danfoss timer in the equation too. This timer has 3 settings, water, water and heating and off. I am going to connect the water only option to the pump only, the water and heating to the boiler and pump.

The system I currently have does not have any connection to the hot water, this is from a mains pressure tank and electric heating.

What this will give me when on the 'water' only setting is the ability to switch the pump on for 2 separate 1 hr sessions. This will eliminate cold spots in the water system and also help reduce the risk of pipe freeze as flowing water will not freeze so easily.

When I am resident in the place I can then switch it to full heating on the timer unit