5

I live in an apartment with central water heating and a wall mounted Honeywell T822K1034 thermostat. I've had this thermostat before, and as far as I understand it works on the principles:

  1. It has a spiral thermometer to measure the indoor temperature
  2. When the indoor temperature falls a few degrees below a target temperature threshold set by the control lever, the thermostat completes a circuit in the wall, opening a valve in the unit and letting heat in
  3. Once a the temperature rises above a few degrees higher than the target temperature, the circuit is broken and the valve is shut off, stopping the heat

T822K1034 wall mounted thermostat

However in my unit, it's failing to maintain the set temperature, and instead acts as a manual valve switch where you move the control lever to the left to turn it off and to the right to turn it off.

enter image description here

Based on this behavior, I'd guess that the wires are switched. Opening it up, red is connected to R (power) and white is connected to W (heat). Assuming that red is hot and white is neutral this seems to be wired correctly?

So far maintenance says there isn't a problem. They claim that the thermostat can't maintain an indoor temperature because "the boilers temperature is controlled by the outdoor temperature". This doesn't seem relevant to me, since the point is to control not the temperature of the heated water, but the flow through the pipes into the unit.

What am I missing here? Is it possible to have this thermostat maintain an indoor temperature or do I have to manually switch it on and off when it gets too hot/cold inside?

EDIT: This is in Ontario, Canada

11
  • 2
    Boiler water temperature will determine how long it takes to heat your apartment to the desired set point, not whether it will heat at all. I'm really not an expert here, but it sounds to me like your thermostat isn't working correctly and that maintenance doesn't want to fix it. I'd suggest talking to a few of your neighbors to see if they're having the same issue, and if so, present a united front to management. Also, management may not be aware that maintenance is putting this off, so you may want to contact someone else...
    – FreeMan
    Dec 1, 2022 at 16:41
  • 1
    Your question is written very clearly but can you confirm that the heat comes on when you move the temp control to the left (lower numbers) and turns off, when you move the control to right (higher numbers)? If so, then something is definitely backwards. Also, what's going on with that black wire? I can't make out whether it is connected to anything.
    – JimmyJames
    Dec 1, 2022 at 16:52
  • 1
    You should probably confirm your location. I'm guessing you are not in the US given that the temperatures are in Celsius. But assuming that's not a factor: red is power, white is the connection to the heat source. Black appears to be C or common and I'm reading that it is usually associated with heat pumps. It might not matter here but is this a forced water system or a boiler?
    – JimmyJames
    Dec 1, 2022 at 17:07
  • 2
    @rovyko It appears to be wired correctly, at least red/white. I doubt it would work at all if they were switched somehow. You could damage the thermostat or the furnace if you flip them. I once fried a Taco pump doing it wrong.
    – JimmyJames
    Dec 1, 2022 at 17:13
  • 1
    If your maintenance people can't understand that moving the setting to cold brings on the heat and setting it to hot turns it off is not how thermostats are supposed to work, they are idiots or lying. Call management.
    – JimmyJames
    Dec 1, 2022 at 17:18

2 Answers 2

6

Bang-Bang Controls 101

Based on this behavior, I'd guess that the wires are switched. Opening it up, red is connected to R (power) and white is connected to W (heat). Assuming that red is hot and white is neutral this seems to be wired correctly?

Close. These are 24-volt "low voltage" controls. Which means hot and neutral are not applicable terms here, but you're on the right track. The standard wires in 24-volt systems are:

R = 24V supply from transformer (hot-ish) C = 24V return to transformer (neutral-ish) W = call for heat G = call for blower only (in forced-air systems) Y = call for air conditioning

Sometimes the A/C unit has its own 24V transformer, that's why there's R(h) and R(c). You can see those unpopulated sites right in the plastic molding of your thermostat. B and O are heat pump things.

Back down in the guts of the system, there's an actuator (gas solenoid valve; Taco water valve) that is wired to W and C, completing the circuit. The thermostat doesn't get C unless it is a Nest. Note the spare wire for if that ever happens.

So far maintenance says there isn't a problem. They claim that the thermostat can't maintain an indoor temperature because "the boilers temperature is controlled by the outdoor temperature". This doesn't seem relevant to me, since the point is to control not the temperature of the heated water, but the flow through the pipes into the unit.

You got it. At some "low" setpoint, the thermostat goes BANG! on. And at a high setpoint it goes "BANG!" off. But think about it: A Bang-Bang controlled heater, when it runs, must run hard enough enough to overcome the worst arctic chill possibly expected in this locale.

So in your mind, you are expecting your building to deliver Very Hot water, hot enough to overcome the worst possible Polar Vortex, and on a temperate day of say 13C (55F) you'd run maybe 5% duty cycle. You don't dare shunt R and C (set thermostat to max), or you'd be smoked out of the apartment! That's your expectation.

And.... that's obsolete.

Except the Bang-Bang approach is obsolete. It made sense when gas or electricity was cheaper than smart controls. But now, it's no problem running a furnace at variable speeds - and this enables technologies like condensing furnaces which gain 15-20% efficiency over Bang-Bang units, or VFD-controlled heat pumps which are quieter by a lot.

In this scenario, the furnace runs pretty much continuously at the lowest setting that will do the job. It figures out what that is by looking at outside temperature and from that, estimating how much thermal loss your house is having through insulation and leakage.

In that light, what maintenance said explains everything. Your building has converted to a condensing boiler, which runs the system hot water at a variable temperature based on outside temperature. It is trying to supply exactly the right temperature to your radiators to compensate for thermal losses through the insulation.

So if your apartment had no thermostat at all, one could reasonably expect apartment temperature to follow the weather, but stay halfway reasonable. You can try this for yourself simply by setting the thermostat to "MAX".

However, if that results in an apartment that is warmer than you'd like, the thermostat allows you to do BANG-BANG control of that already-adjusted heat. Because the heat is close to optimum already, the duty cycle will be much longer - say, 90% on a 13C (55F) day.

This also imposes a simple maximum on how hot it's possible to make the apartment.

3
  • 1
    This makes a lot of sense, unfortunately the "right temperature" supplied to my radiators is way too hot, leaving the unit at around 28C ambient if the valve is left open continuously. Since the valve IS controllable (I'm able to turn the heat on/off) and the radiator output is hotter than ideal temperature, the same principles apply. The thermostat should simply switch the valves less frequently, since the incoming heat approximates the ideal unit temperature. So far I've left the window slightly open in the bedroom, but I still have to fiddle with it daily to keep the unit pleasant.
    – rovyko
    Dec 2, 2022 at 4:16
  • 1
    @rovyko ...well that's how they should set it up. Have it run a little hotter than ideal, so you can turn it down with the bang-bang thermostat. It sounds like your thermostat is either broken or not very accurate. FYI they're like $40. Not even. Dec 2, 2022 at 6:18
  • Yes I just misread the last part of your answer
    – rovyko
    Dec 2, 2022 at 14:14
3

Feel free to pick holes in this theory, as much as you like. I'm just guessing… & I'm using the answer space for illustrations.

I'm starting by assuming some physical relationship between the "knob" & the unit marked 'Precision Switch' & that the device is managed by a bi-metallic strip round the 'knob', at a variable distance, based on distance from the rotation centre, around the circumference. If that's incorrect, then the entire theory falls at the first hurdle & I shall beat a hasty & apologetic retreat ;)

I have to admit I really know nothing about this technically - however… if the lever below is how you select your temperature, then currently it's set at 'hottest'. If you move it towards coldest, the "knob" above will first present its open face to the 'Precision Switch' then eventually the opposite end of the scale.

I'd say the "knob" is misaligned.

By way of illustration, & to make this easier for my limited Photoshop skills, first I roughly perspective corrected the image

enter image description here

Then 'turned the dial'

enter image description here

Isn't that going to break contact with the 'Precision Switch'?

I suppose a quick confirmation would be to see if a neighbour will let you photograph theirs to check the alignment. Saves getting building maintenance out again to scratch their chins.

2
  • 1
    Good catch, sir!
    – FreeMan
    Dec 1, 2022 at 18:05
  • 1
    Very nice photoshopping ;)
    – brhans
    Dec 1, 2022 at 18:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.