How does a typical heating system controls work?

[Alexandre Verri]

I bought a house in Ireland two years ago and I still have some doubts about how the heating system controls should work.

My house has one thermostat and also a programmable mechanical timer. This is what I refer here as the control system. The actual behaviour of the control system is:

Regardless of the programmed timer, if the room temperature is less than the temperature set on the thermostat, the boiler and pump start working to heat the house.

If the room's temperature is bigger than the temperature set on thermostat and the timer fires, the boiler and pump start working to heat the house.

It seems a strange behaviour, this is not what I would have designed. I would prefer the following:

If the room's temperature is less than the thermostat and the timer fires, the pump and boiler should start working.

Please share your thoughts on this, how is your control system?

[Tekkie©]

On Sat, 20 Feb 2021 03:05:37 -0800 (PST), Alexandre Verri posted for all of us to digest...

I am taking a SWAG here: I think you want to set the timer and it's temperature to when people are actually in the house and awake.

The other setting is what I would call a 'sleep mode'. Some people like the temperature cooler when they are asleep or the house would be vacant for a significant time.

You probably have what is called a programmable thermostat. I am in America and not familiar with Ireland. Although I would like to travel there and have ancestors there. I have reposted this to the newsgroup group called alt.home.repair in the hope that you will receive more thoughts. Please subscribe and join us there.

[micky]

It's conceivable that they put the parts together wrong Conceivable, but very unlikely. It coudl be that the timer should control the pump and boiler like you want, though I'm not sure what would happen when tthe timer is ... off, is that the other setting? Would the house get really cold if the timer were off and that stopped the boiler from working. Or does the timer somehow change the temp setting like one of the ansers though could be the case.

Be absolutely sure you have a totally understandable drawing of how it is connected now so you can put it back that way when you realize you've made it worse. But maybe you'll make it better.

Don't depend on your memory. It's amazing how easy these things are to forget in only a few minutes.

Take photographs and make functional drawings and schematic drawings and then stare at the schematic until you understand how it is set up, what the timer is supposed to do (and how it's supposed to do it) (It seems pretty clear what the other parts, the thermostat, pump, and boiler are supposed to do.) And when you know what the timer does and what it's role is supposed to be, then you'll know if you can rearrange things or not

What about other houses on the street? Or anywhere in town? Do they have the same setup? This is a good way to meet your neighbors. If uou ask to see his furnace, he might turn out to a pro or a long-time owner who can tell you what's wrong.

I had a room air conditioner and when the thermostat said was cool enough it stopped the compressor, but the fan ran constantly. If it cooled off 30 minutes after I went to bed, the compressor would stop but the fan would run all night. I hated that. I hated the noise. All the connections were slide-clips and I only had to rearrange 3 of them so that when the thermostat said it was cold enough, the fan and the compressor stopped.

The designers don't like this because there is no fan to circulate the air so that the thermostat knows almost immediately when the air is too hot. But I don't care if it has to wait 30 or 60 minutes to find out.

Is it possible the timer was added by a previous owner, not by someone skilled in heating? That would make the chance of it being wired incorrectly a lot higher.

[Scott Lurndal]