Radiators are hot when heat is off and hot water tank is running. (Please Help)

Risdoid

I live in New England and have oil heat with a boiler and a hot water heater under 10 years old. I have the boiler serviced annually. Recently, I noticed that the radiators are getting hot (136 degrees) when the heat is off. This happens when the hot water heater comes on to reheat the tank. The Honeywell thermostat was installed by a plumber and is functioning correctly according to Honeywell's customer service team. I did have an annual service on January 10th and had an HVAC company come out in February. They said a vent on the return was plugged, which they replaced. They emptied a lot of rusty water until the float glass was clear and used extension drill bits to clear a vertical return pipe. They told me that the water in the pipes is toxic and causes the pipes to break down, leading to water hammering and system overfilling. They said I should consider a new gas wall-mounted furnace and baseboard heat. That's cost prohibitive. The house was built in 1937 so I find it hard to believe that I need new iron pipes throughout the house or a new heating system. I am considering having a plumber flush the system, but I want to be sure this does not cause leaks or more problems. Any advice is greatly appreciated. Thank you.

Intplm.

@Risdoid
I have some idea as to what might be going on with your system.
You say you have a boiler. Is it steam heat or hot water heat? Im guessing it's steam? But I would rather be sure.
Can you post a few pictures far enough away and some closer to get a better idea as to what you have?

Jamie Hall

Most of what your "service" company told you is pure baloney. You need a company which actually understands steam heat (which I'm almost sure you have).

That said, likei @Intplm. I have a pretty good idea what the problem is (and I'd bet we both have the same idea) -- but pictures would help (and, by the way if it's what we think it is, it's a cheap fix...)

Risdoid

I have steam heat with cast iron radiators. I am out of town and will take photos when I return. Appreciate your replies.

Risdoid

Here are the photos of my Thermoflo Boiler and Hot Water Heater. Thanks, everyone.

Jamie Hall

Love to help, but that's not a format my old machine can read...

HVACNUT

I don't think the pig tail on the horizontal is right. There's probably water in the loop preventing the pressuretrol from reading the actual pressure. 
Also can't see where they tapped off for the indirect. 

Jamie Hall

There does need to be water in that pigtail for the pressuretrol -- that's the whole idea. That installation is a little unusual, but fine.

Somewhere in the controls there should be an aquastat. It will be wired in parallel with the thermostat for the house, wherever it is. It senses the boiler water temperature, and keeps it hot enough to make hot water, but not so hot as to make steam -- and the odds are very good indeed that it is misbehaving and allowing the boiler water to get too hot, making steam, which then gets yr radiators hot. See if you can find that and maybe a picture of it?

mattmia2

I can't open those images either.

Most likely wherever the aquastat is it either is in an air bubble, is broken, or someone turned it way up while servicing something and didn't put it back.

HVACNUT

Jamie Hall said:

There does need to be water in that pigtail for the pressuretrol -- that's the whole idea. That installation is a little unusual, but fine. Somewhere in the controls there should be an aquastat. It will be wired in parallel with the thermostat for the house, wherever it is. It senses the boiler water temperature, and keeps it hot enough to make hot water, but not so hot as to make steam -- and the odds are very good indeed that it is misbehaving and allowing the boiler water to get too hot, making steam, which then gets yr radiators hot. See if you can find that and maybe a picture of it?

Thanks Jamie. I always thought there was only steam pressure (or not) in the anti siphon.
These are the pics the OP posted. I don't see an aquastat on the boiler so when the aquastat on the indirect calls, the boiler is running on pressure, not temperature. 

mattmia2

The aquastat could be on the piping to the coil in the indirect too and we can't see most of that.

Jamie Hall

There may be two aquastats. One to tell the circulating pump that the indirect needs heat -- but the other to control the boiler maximum temperature which shoulld, as @mattmia2 said, be on the coill in the inderect -- possibly a strap on type on the pipe, or even in the boiler itself. What should happen is the indirect calls for heat and the circulating pump comes on -- but not necessarily the boiler. The boiler should only come on if its water is cooler than the indirect needs. That's the second aquastat.

Steamhead

I don't think the second aquastat is even there. Following the wires from the Taco relay to the primary, they appear to go straight from one to the other with nothing branching off.

The boiler itself is a rebranded Weil-McLain SGO. That pigtail arrangement is used on the SGO version also, and it's fine, but we often use a 270° brass pigtail there as it's less likely to clog. The SGO version has a 1/2" tapping below the one where the pigtail is mounted, which we often use for a secondary LWCO probe but could be used for an aquastat as well. On this one, we'd have to loosen the front of the jacket to see if it was actually tapped- if so, that's where the aquastat can go.

mattmia2

It cold be a strap on aquastat connected at the tank with the tank aquastat with a 3rd wire to the tank.

We need to see the back of the boiler and behind the indirect.