Switch on and off Lp gas burner based on water and room temps

Instead of manually switching on or off my LP gas boiler, have the water temperature limits and room temperature limits control it more efficiently. Don’t need the water heated to 145 degrees on not so cool days
Need help with selecting hardware RaspPi-ware and some programming 2023-12-08T06:00:00Z2024-01-31T06:00:00Z


Hi Will
145º?? Would have to be Fahrenheit you would really struggle for 145ºC. Would be steam over 100.

Beside all that you need to know exactly what happens when you turn your boiler on and off. Obviously the gas turns on and then is ignited. There would have to be some safety arrangement that shuts off the gas if ignition fails somehow. You would need to know how this is done. And don’t say “I just turn on a switch”, you really need to know what happens when you do this.

BUT. Be VERY careful. An acquaintance of mine blew the front of his house out by playing with a gas heater he knew nothing about. Lucky to get away with minor burns.

Don’t know about Chicago but here (Australia) we have some very strict licensing requirements for tradesmen who deal with Gas. Of course there is nothing stopping Mr Average Citizen from playing with any of this but don’t bother with insurance claims if anything should go wrong.

I am not trying to dampen your project but even if you get something working OK for now and something goes amiss some time later Any insurance company would write you off if you have modified an installation in any way. These people do not like paying out money if they can get away with it. Depending on the laws in your location you could also be in trouble for interfering with such an installation.

Although I believe this is doable with the hobby and maker devices covered here I would be reluctant to try myself. Put it into the too dangerous basket and find a commercial approved product to do the job.
Cheers Bob
Add on
And if it were here we would have to get a plumber with a gas licence to fit it.


Thank you Robert
Good points you made all the way round
I could get a professional to see how the device works , with safety in mind


I had a furnace professional put an in line switch on my LP boiler to activate/on and de activate/off the system
It’s been working well to cut the usage.
Now I’d like to replace switch with a RPi using pipe temperature sensors, etc.

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Hi Will
While RPi gets lots of mention and publicity (some good, some bad) I think it is still a development/experimenter kit and personally I would not think I would trust it with something to do with gas switching.
But that is just my personal view. At the end of the day it is up to you. But I urge you to be very careful.
Cheers Bob


Thank you Robert
I really appreciate your kind concern.
I’ll continue to consult with others more familiar than my self.
More info leads to better decisions, right?
Thank you again.


Hi @Will243138 - I can’t guarantee that any staff at CE can weigh in on this one due to the nature of the project, but it won’t hurt to share some pictures so we know what we’re dealing with. It sounds like your approach is sound since the plumbing has been done professionally and you just need to provide a control signal to off the shelf devices and assuming these devices can be expected to operate safely regardless of the control signal state.

FYI we stay away from mains projects (electrical and gas) in general

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Thank you for your response to my post.
I certainly understand and appreciate your concern for my project. It really could have dire consequences if handled improperly.

I’ll be visiting with some gas professionals soon to run it past them for added insights or concerns.

I’d like to replace a manual switch with a micro processor switch and at the same time down loading on/off times, water temps., room temps., outside temps., wind chills, etc., plus a display.

I can throw the switch, turning off power to relay, when the house is warm and outside temp. is above say 30 degrees. (0 C).

Thank you, Michael
I look forward to further posts

Hi Will

OK, you just want to replace a manual switch with relay contacts controlled by a micro processor (RPi etc). That should not interfere with the gas operation. s long as you stay away from any thermostat operated controls etc and confine this to “master” switch type operation. But to do this I assume your gas system ignites automatically when this switch operates.

The system must be “fail safe”. That is in the event of a micro failure it fail to a safe condition.

The RPi I believe is a development and experiment type platform and should be treated as such. I know some use them in permanent or semi permanent situations but usually (or hopefully) in non critical scenarios. With that in mind I would not discard the manual switch but use relay contacts in conjunction with it.

If wired across or in parallel with the manual switch this would be OFF in normal operation with control by relay which must fail to the OFF position. Wired to the NO contacts so in the event of a micro failure the system could revert to manual operation. This would be my preferred option as the electronics could actually be removed completely if required while still allowing manual operation.

You could wire in series but this becomes a bit messier. The fail safe would have to fail to ON condition with the manual switch in ON position for micro operation. The relay would have to remain in situ for manual operation with the wiring to NC contacts. to as safe as I would like it.

A parallel connection I think is the safest by far as if there is a failure everything is OFF.

All the monitoring and displaying of details is a separate thing altogether.

Cheers Bob
PS: If temps above 30ºF is considered warm and you live there ???

Thanks Bob
We’re experiencing unprecidented warmth this winter season (near 50F). Also no snow on the ground most of the season, very strange.
Last winter, nearly record snowfall.
(1972 Jan. 15 -56F no wind chill)

Thanks for the verbal info. Very instructive. Would you be able to draw up a schematic for me to consider (holding you harmless) to make sure I’m following you properly?
I like the fail safe method, indeed.
Look forward to more input. Thank you.
G’day, Will

Hi Will
As requested here is a small sketch of what I described. The relay could be a Transistor, Mosfet or one of the relay modules readily available. The choice is yours. In operation the manual switch should be in the OFF position and control will be passed to the relay contacts.

The circuit provided is a means of transferring manual ON/OFF switching from the switch to controlled relay contacts. Nothing more.
I cannot be held responsible for any malfunction or damage of any description resulting in the use of this circuit.

Be aware the circuit above and any controller(s) should be considered an ignition source and the appropriate measures taken as laid down in any rules regarding ignition proximity applying in your state or territory.
Cheers Bob
PS: -56ºF (-49ºC) ?? Not fit for human habitation. Currently about 35ºC (95ºF) and getting hotter here.

Thank you Bob for the schematic,
Great care will be taken if I decide to pursue this further.
Greatly appreciate your knowledge and concern!
I hope to continue conferring with you and Core E.
Turn a fan on if it gets too hot there…
Thanks again!
Sincerely, Will