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Disconnect the zone valve wires and test the system with a hot water call. If it still gets hot it has to be the zone valve. One thing to note if you have power stealing thermostats A1 should go to your R terminal on the thermostat subbase. Polarity is important and can affect the manager. Also if there is no common wire used it can create ghost calls with just enough voltage thru the manager to give you this problem .

You can dm me if you need further help

I don't have the manual either — but if it's more or less typical and on a 15 amp fused circuit, I'd make a quick guess — probably close enough — that it draws somewhere between 500 and 1000 watts running, and around 1.5 kW starting (briefly).

Two things to consider on the battery "generator". First, check the surge output capability. It must be at least 1.5 kW. The second, though, is this: either unit you mention, if they have the surge capacity, should be able to run the boiler. For a while. Remember that unlike a fuel fired real generator, these things are really batteries with an inverter — and when the battery goes flat, that's it. You can't just pour in more gas and off you go. With the larger unit you mention, and the smaller draw I estimate, you'd have no more than 4 hours of operation — and going the other way, you're down to one hour (powering nothing else). Is that long enough to cover your needs?

Edit: I notice that the Jackery web site cheerfully notes that when the battery goes down you can recharge it from solar (with the sun out and a good big array) or a USB port (but what is powering that?) or plug it in (to what????)

The closer spacing give you more consistent slab temperature, good for baths to use 6". You feel a wide temperature spread wit 12" min bare feet.

It also gives you higher btu/ ft output, quickens response and allows for lowest supply temperature. I run an A2WHP so low temperatures drive the HP efficiency up.

The depth of the tube matters also. I had thought I did a better job getting the tube 2" below by raising the mesh on foam blocks. You really need to use continuous bar chairs every 2' to assure the mesh stays up into the pour. That adds a lot of steel cost.

Tube 6" OC and into the slab can drop your supply 10 degrees or more. See below charts.

For my own slabs I always do 6" oc. It can be done with 1/2" pex if you light bulb the ends.

This slab as poured several years ago.

I like these Viega PureFlow couplings for non-PEX A tubing. (Thank you @kcopp.)

I'm adding a bath to the read of my shop space to create an ADU.

Unfortunately I needed to cut a utility trench through a slab that is only a few years old.

I do want to retain the radiant heat so I came up with a method to re-attach the cut loops.

The loops are 6" OC so it required a number of couplings, and some concrete sawing.

These 12" electric hand concrete saws work amazingly well. I used a gas powered walk behind sam for them long cuts. The hand saw was just as fast to cut, actually.

I used the wet saw to cut parallel to the loops first. Then a cut across the tube about 1-1-2" deep. The piece came out easily with a chisel. Luckily concrete doesn't stick to pex, so the tube was undamaged to reconnect. This provided just enough room to get a crimp tool around the tube.

I can slide some insulation below the tubes, some rebar to keep the pour stable.

@twbrkfd1

Would love to see a picture of that thing. Asbestos and all haha. My 1937 No. 7 boiler is a champ. This past heating season was no different.