Boiler keeps on shutting down with high heat light

Are you saying the boiler shuts off because it over heats? That's what I get from the title. If so will it start when it cools? If I had to guess? It's air bound somewhere. Maybe post some pictures of the system so we can see the guage and the piping.

A system with purge valves! That's wonderful! To purge each zone is simple: close the manual valves on all three zones — the ones just above the pumps. Pick a zone, put a hose on the handy dandy drain valve on that zone, open that valve and run water through the zone using the manual system feed valve if you have one, or figure out how to run from that drain valve to your doemstic water. You need a lot of water. Run that zone until you get no air. Repeat for the next zone… close the purge drain valves and reopen the valves above the pumps and you may be good to go.

Did a professional replace the tank and the valve?

Hydroair coils are very prone to getting air bound if not purged.

@JonathanUpstate

Shouldn't bad mouth the plumber. You did some work and then called him in to fix the problem. Yeah he should have looked into it a little more. He had no way of knowing the system wasn't bled. Most in the trade do not want to touch homeowner work.

It creates a huge liability risk for the plumber.

Picture this as I had a coworker who was licensed involved in this situation doing a side job and he had a permit:

Homeowner does some of his own wiring in an attic. Then he calls an electrician to fix an unrelated problem in the kitchen.

Two days later the house burns to the ground due to an electrical fire in the attic.

Who is at fault?

The electrician unfortunately is in for a tough time. No more "innocent till proven guilty" he is the last one in the house with a license.

CPVC is rated to 200°F is that acceptable for a boiler relief tube? Sharkbites are also rated to 200°F.

It would seem neither CPVC or Sharkbite fittings are suitable based on the boilers aquastat and hi limit temperature settings?

A 3/4 male by compression is another option if you want a DIY fitting. Or have HD thread a piece of steel pipe the correct length.

Here is the ICC code

It is not uncommon for the high limit to be set 20° over the operating temperature on the aquastat, so 200° hi limit, 180° operating.

Although we see tankless coil boilers operating at 200° come across this list commonly. I think most high limits go to 230 or 240°F.

Low ball fin tube bids often ran the fin tube at 200° to cut down on the amount of baseboard they needed. That higher operating temperature was also part of the IBR Hydronics Institute training years ago.

If you have a torch and know how to sweast copper do that. If not go to HD or a supply house and buy the fittings you need and have them cut you a piece of pipe or make it up with nipples and couplings.

Don't leave a thread on the bottom end of the pipe

If I saw what you described above, I would assume that a homeowner that has not clue did it. I would change my way of piping in relief valves if I were you. You wouldn't want other professionals thinking you are not a true craftsman at your chosen trade. But that's just me… (and a few others it seems)

You are absolutely right ALL high limits are set to 180° on ALL heating boilers, unless that are not. And many of those 180° high limits are adjustable all the way up top 240°!!!

But you are probably right about every one of them being set at 180° unless they are not set at 180° for some reason. I myself have set some high limits at 210° because some other professional or DIY installed didn't install enough baseboard heaters in a home to make the home 70° when the outside temperature was -12°F (twelve below). You see, in my part of New Jersey the recommended outdoor design temperature is 14° above zero. So when you get the occasional -12°F for 3 days in a row every eight years or so, and you have no time to add more radiators, you do what you have to in order to get the heat to work.

Now after that, you offer to add more radiators for $$$.00 and see if they want to fix the problem. Often those customers have the problem because they didn't choose the higher price job to begin with and have an inferior system as a result. So they choose to leave the limit set at 210° because the higher fuel usage caused by the higher limit temperature happens in small increments each day, adding radiators cost $$$ all at one time. They are paying one way or the other but can't see the forest for the trees.  

@JonathanUpstate I'm sort of a perfectionist and the guys that worked for me thought I worried about the details a little too much, so maybe your system works just fine but if you are the electrician that decided to use the green Taco SR503 (green) relay box, you could do better. If you paid someone to do this, then don't call that guy back ever!

From the looks of this picture, you may have 3 zones, two for central heating and one for hot water.

OR

That tank is a separate electric or gas or propane water heater and you have three room thermostat zones.

Regardless of the zoning situation, that low voltage (thermostat wire) wiring has a lot to be desired. As long as it works, don't touch it. No one from tne neighborhood association will be inspecting this and grading you on how nice it looks. Spend your $$$ on that flat of annuals and a bag if mulch from the nursery to make the outside look nice. Spring has sprung!

the code says "approved for the temperature of the system", not "approved for temperatures that could exist if the system is worked on by someone that doesn't understand what this clause says or how the controls work". i wouldn't use vinyl. this isn't 1935, there are plastics that are both ductile and can withstand high temps.

It looks like separate relays were replaced with that taco zone panel relatively recently, but if that was with the flip or earlier is hard to tell. it certainly is newer than the circulators which might be older than the boiler.

neither the circulators nor the boiler are anywhere near that old.