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Re: House heats up but thermostat is turned off AND thermostat's battery is dead

@HVACNUT, @mattmia2, @ethicalpaul, @Jamie Hall I'm not at the house now so I can't do anything. I'm waiting for my Taco 5000 valve body to arrive (hopefully today) and then I'm going back (hopefully tomorrow) to assess and correct. I will do what you suggest, put C1 back and disconnect TT.

Here's a conversation I just had with ChatGPT about this mystery. None of you will be surprised by it.

Me to ChatGPT:

I went back to the house to adjust the Hi and Lo temperature settings. In doing so I momentarily turned the LO setting to 140F or below. When I did so, I heard a soft click. I then set the controls where I wanted, the standard 180F for Hi and 160F for Lo. I then leave the house with the boiler turned on. Hours later I get a text from the resident telling me the heat is on in the house. But that the thermostat has been turned off for a week and the battery is low if not dead. What happened?

ChatGPT said:

Thanks, William — I’m with you. Based on your description, here’s what most likely happened:

🔧 What Likely Happened:

When you turned the LO limit down to 140°F or below, even momentarily, the circulator control logic in the Resideo L8124C1003 may have activated.

This aquastat has a feature where:

If the LO setting is set too low or the LO limit is momentarily crossed, the system can engage the circulator independently of the room thermostat, especially when the tankless coil is in use or believed to be.
It may interpret this as needing to maintain domestic hot water temperature and begin cycling heat.

Meanwhile:

If the thermostat is off or has dead batteries, it won't be able to call for heat, but the aquastat can still independently drive the burner and circulator under its low limit maintenance logic.

🧠 The Soft Click:

That soft click you heard was likely the internal relay or bimetallic switch reacting to the low temperature setting you dialed, triggering the burner or circulator.

🔁 What Happens After:

Even though you returned the settings to 160°F/180°F, that brief dip below 140°F may have:

Triggered a heating cycle under the aquastat’s low-limit logic.
Caused the system to begin heating (especially if the boiler temperature had dropped slightly below the set LO during your adjustment).

And because the aquastat doesn’t rely on the thermostat for this part of its logic, the heat turned on anyway, even with the thermostat turned off or failing.

WilliamJ

0

Tank size?

I was just asked to hook up the radiant floor heat in a partially finished home. Apparently towards the front left area of this house it has concrete slab floor covering a 16 x 20 room with a 12’ ceiling. In the crawler two 1/2” pex lines stub into it. A supply and return.

He has a 50 gallon electric HWT and an electric tankless (that I don’t have the make, model etc on) in the laundry room about 15’ away from the room with the slab. The load on the hot is two full baths, clothes wash., kitchen sink w/dishwasher. Can I use the 50 gallon tank for the heat too?

johnraymond

1

Re: Learning from the 1930s

A properly designed gravity hot water or steam heating system will have a much, much, longer service life and cost less to own over time.

leonz

1

Constant Circulation Piping Layout

Hello. Thanks to everyone in advance for anyone willing to take a look at this. I have been working on my layout for my CU3A boiler and 79g Viessmann indirect using Runtal radiators (roughly 20) of them for our retrofit for our 1880's home in Boulder, CO.

I think I have it figured out and I have spent time thinking about the location of the check valves? I wondered if the Quicksetters on each manifold branch are a good/helpful idea or should I scrap them?

Certainly would appreciate any input regarding the layout and any mistakes I may have made. Thank you

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Amovida

0

Re: Once Upon A Time, In The White Mountains of NH....

Although "educated" with a mechanical engineering degree and well grounded in the trade of carpentry. Elegant solution is a term often used, that came to full understanding after successfully planning, installing, operating the steam replacement for the previous replacement done, quick and dirty with copper, dangerously lacking the Hartford loop that led to its demise. Having long ago expanded my skill set beyond carpenter steam remained a mystery otherwise I would have recognized and repaired that dangerous piping. I am off topic here, but as Jen would say "circling back", the denial of firing that boiler reminded me of my awareness and astonishment at the quiet, tranquil, delivery of steam heat. That elegant outcome resulted from the extensive research and acquisition of knowledge I was aware I lacked, like the Hartford loop the reading of your knowledge sharing posts revealed the need for so much more.

This is my long winded way of acknowledging this demonstration of heating elegance, and once again extending my gratitude to the steam heads for teaching me to recognize and appreciate craftsmanship at the highest level. Thank you

geo_1111

0

Re: What would cause such rapid destruction of valves?

Speaking as a homeowner,

Galvanic Corrosion, also known as bi-metallic corrosion caused this.

If you are going to keep this plumbing as is-

When replacing the parts you should be using bronze fittings/pipe nipples etc. all the way back to the heavy wall pipe and tees, and a bronze shut off valve and bronze pipe nipples to shut the boiler water off from the pressure regulator as you should only be filling the system ONCE and shutting the water off and leaving it off. You also need a back flow preventer piped before the water feed and pressure regulator.

leonz

0

Re: turbo torch tip sizes

I never used to look at the recommended sizes.

I used turbo torch tips and have a pile of them, Even used the turbo torch propane we owned a few of those at the shop I worked at propane being much cheaper than acetelyne.

Sometimes we were soldering or brazing indoors sometimes outdoors in the winter on a roof with wind. Sometimes you had a valve near where you were brazing that you couldn't overheat. Sometimes you need to solder fast or slow. All those things affect tip size.

I prefer the old prestolite tips for smaller stuff as I don't like the "turbo noise" and prefer oxy-aceteylene for brazing but you can't always justify setting that up to do a couple of joints

Just my rant.

I am probably a slow solder, I prefer to use a smaller tip and take more time but there are times this won't work and you have to speed up. It's all a judgement call in the field. Maybe fabricating in a factory is different.

EBEBRATT-Ed

3

Re: Boiler with indirect water heater only

That's a LOT of hot water. But if that's what it needs, yes just pipe it direct to the boiler in 1-1/2" with a Grundfos 26-99 or equivalent and wire the circ to the orange "DHW pump" output in the junction box underneath the boiler. You can adjust the post-purge time in the settings but they are 30 seconds or less from the factory, I have never timed it. No harm in letting it post purge a little bit to scrub any excess from the exchanger. Easy peasy.