Tankless Coil Intermittent Hot Water

He set the boiler at five cycles per hour to eliminate any cooling of the water in the boiler. It was always above…………175°………….give or take.

At 1 cycle per hour…………..now it cools down below………….140°…………and that's insufficient for a shower considering the heat transfer of the tankless coil.

The boiler needs an aquastat that will maintain the boiler at 180° consistently, independent of the heating demand. This is acceptable in the heating season but is highly inefficient for the remaining six months.

I'm not grasping the "then warms up again" statement. Be curious to know if the boiler started at this moment………….and, if so………….did the thermostat call? I tend to doubt it because you'd have consistent hot water for at least 15 minutes.

You could also try a low cost experiment and set the boiler at 3 cycles per hour. This might provide acceptable HW for most showers but you'll notice a drop in the temperature of the shower if you started the shower at the end of a boiler cycle. A lot of this speculation depends on how much water the boiler holds.

All of the above, other than a new aquastat depends on the boiler actually running 3 cycles per hour. If a thermostat is controlling it, it MAY run three cycles per hour………….or it may not run at all if there is no heating demand. If this is the situation, you must install the aquastat. If outdoor temperature climbs to………..say 45F…………the boiler might run once every two hours………….independent of the claimed 3 cycles per hour.

What model aquastat? If it's an L8124***, then that aquastat maintains Low limit, and only will run towards High limit with a heat demand. So if you're raising the High to 180°, raise the Low to 160°. Differential 10° unless you really want to get into it. Be careful at the faucets.

If the aquastat is an L8041B or equivalent, that aquastat maintains High limit, but I would bring the Low up to 145° considering a pre set 10° differential.

Again, faucet adjustments will be different. Is there a mixing valve?

As EPaul alludes, the boiler coils are not very efficient, are difficult to control and often clog with lime in many areas. You'll probably be happier with an indirect hot water tank, or separate tank hot water heater.

If you keep the hot water coil, it should (must) be plumbed with an automatic tempering valve to prevent it from delivering dangerously hot domestic water when the heating system is steaming. Many installers skipped the tempering valves or substituted a manual valve to save a few bucks. Especially with kids or elderly folks in the home, overheated hot water can cause serious injuries.

under that cardboard are 3 screws, common, normally open, normally closed,

a volt meter across common, and NO, or NC, would tell you where your volts are going, listening closely will swinging the setting dial you should also hear a click,

Yes. Sorry, I feel dumb assuming you had a closed hydronic system. 180° should be fine and the differential is at 5° so there shouldn't be an issue. Can you show the coil or water heater and piping? Is there a mixing valve?

Not dumb at all. Just need a bit more information. The aquastat is exactly what is required and you already have it. You have set it to 180°F and that will solve your problem. You can also see a small white dial on the right side near the bottom. It's set at 5°F. Increase this value to 15°F. This will prevent too much cycling of the boiler when the heat is not calling. I'm fairly sure you'll still be OK in the shower………….but, if not………….reduce it to 10°F.

Don't bother with any meters testing anything under the cardboard………..more work that you don't need.

You already have the anti-scald valve which is important with a steam boiler held at 180°F.

Picture of the Watts 70A mix valve is already above.

water level looks good for coil,

130/140 was too cool, careful at 180,

note where the mix valve handle is, then exercise it back and forth a few times, and set back to original position,

careful at 180