Need more consistent domestic hot water

Hi, Thinking is good🤔 Have you considered adding an indirect tank? It would give you more consistent temperatures.
Yours, Larry

Could be the mixing valve.

That being said a tankless coil is only good for 2 people or so if you have more than that I would look at different options.

I am not thrilled with an indirect tank on a steamer. The cost of the indirect and a bronze pump will cost $$$.

If you change the mix valve and coil and are still dissatisfied I would look at a 40-50 gallon electric. You could use the tankless to preheat the electric when the boiler is on for heat.

Unless gas is available.

Also some are not aware of this but tankless coils only put out their rated capacity with 200 deg boiler water and you don't want to go that high

What water temp are you running for DHW in the boiler.

I see no purpose to your flow switch idea as the low limit and the flow switch would have to call for the boiler to run.

What you could do if you had a spare tapping in the boiler and put an additional low limit control in that tapping set for a higher temp say 190. You could wire that control in series with the flow switch and the to the boiler.

So when the flow switch calls it puts the new LL in the circuit to the boiler at a higher temp but only while the flow switch is calling.

But we are beating a dead horse. I would go electric if the new tankless doesn't work.

If you like the way your current tankless works you will like a standalone tankless. They need to be cleaned at least once a year, multiple times if your water is real bad. Still flow limited, and will give the same symptoms your current setup does when they start to scale up.

Sounds great!! Can't maintain temp, requires lots of maintenance, low flow, and prone to scale! Who wouldn't want that?

@Jon Held_2 I think your fear of standalone water heaters is being too heavily biased by one bad event. If you put one in you won't even have to think about it for 10 years, how is that not attractive?

Paul I think you meant that directed elsewhere. I dislike tankless water heaters and am a tank fan 😁

From what you are saying, and asking, "Needing more consistent hot water" . It can help to know how many folks you would like the hot water to accommodate? Your current heating of hot water coil isn't doing what you want.

I would size a stand alone water heater (Conventional, hybrid, condensing.) to help with the needs of your home.Sized to the amount of people using the hot water. At this point in time you do not have that. Steam boilers are great but are not always a good option when heating a domestic hot water coil.

Its the quality and amount of water that leads to scaling and performance issues. Don’t blame that on the equipment

I don't blame the equipment, but I'd never buy equipment that required all that work and expense when there is other equipment that doesn't.

Get a 50 gallon tank heater and put a pan under it piped to a drain or outside.

The pan is required in many areas under code now anyway. That solves your concern and gets you the hot water you want.

I changed the anode rod in my previous heater once and that's all I ever did to it in 9 years and we use a ton of hot water.

My current NG heater I've done absolutely nothing to so far, it's about 3 years old.

I'm not a pro.

Others comments aside, after going through 2 tanked water heaters in too short a time, one with the associated flood, I installed a Rheem branded (Rinnai) tankless heater. Has kept up with the water demands of 4 teenage girls plus the rest of us without issue. 4gpm for as long as you want it.

Annual maintenance is overblown. A cheap pump, a 5 gallon bucket and some vinegar is all that's required. Do get the service valve kit. Makes it a snap.

The only repair I've had to do was clean the proving electrodes once in 12 years.

Install was straightforward, did it in half a day. I think getting the copper HX rather than the stainless one was a good call with our water.

Happy camper, I'll never go back to a tank heater.

I've only seen one Bradford White tankless, and now it's a Navien. IDK the model but it had a self adjusting gas valve. It was 2 years old when I first saw it. This particular model was converted to LPG and kept getting a code for incorrect fuel. You could put it through a setup that took like 18 minutes of self checks and it would run. After a phone call with BW Tech Support to verify all was correct, the board was replaced under warranty. I can't remember the specifics, if anything else was replaced, but the issue continued. Spot on combustion numbers when it ran, but it still lockout on the fuel code again and again. BW recommended another board, so a Navi went in and all is good. Maybe it was just that one heater. IDK.

Bradford White does however manufacture decent stand alone atmospheric water heaters. There's companies that make all sorts of things to alert you if theres a leak and can even automatically shut off the water supply. Technology is cool… if you don't count the beginning of my post.

If the oil tank is buried or old, have you thought about converting the boiler to a gas power burner? What's hooked up to Nat gas now? What size is the meter?

That sounds more like an issue with support not knowing how the product works or brining in an engineer when then needed it than an issue with technology or the product.(or having access to the engineer because they bought it from someone else and put their name on it.)

The ones that keep a little tank of hot water are probably ok if you have a large enough gas supply or live somewhere with relatively warm municipal water.

At 190,000 btu/hr that is also most of the capacity of a standard 250 ft^3/hr gas meter depending on how you design for pressure drop.