Insufficient Domestic Hot Water off Indirect Coil

tcassano87

Have a Weil-McLain Hydronic Oil burner with a domestic coil. Below you will see the description the home owner gave on the issue. After looking at the picture he sent, I don’t see a mixing valve off the domestic just a “tempering ball valve” which I know is required & I believe is the issue. Previous tech told him he need an in direct tank to fix his problem, gave him a quote he didn’t expect(but it wasn’t bad). I’m not to familiar with those aquastats or oil burners but I feel the lack of mixing valve is the issue. Figure you guys could help maybe there is more for me to look into or understand before heading there. No other issues or complains

“my hot water works for roughly 1min, then cools down (water is still somewhat warm though) but doesn't get super hot again until about 5min later of running it (we notice it more when showering/giving the kids a bath)”

ethicalpaul

Propose them a heat pump water heater. See if they have utility and/or state incentives, tell them how they won't have to burn oil all summer and be the hero.

People will say "omg no, heat pumps are unproven technology" and yet people come here all the time with direct coil and indirect problems all the time and no one (except me) says anything 😅

hot_rod

https://forum.heatinghelp.com/discussion/comment/1844893#Comment_1844893

I think a number of boiler pros here have suggested tankless coils are about the worse way to generate DHW, although not as eloquently as you have😉

ethicalpaul

Apologies, that was a little intense on my part. Anyway just something to think about!

tcassano87

https://forum.heatinghelp.com/discussion/comment/1844893#Comment_1844893

I know it’s not the best system, but I know they aren’t looking to spend a lot based on not being happy with the previous quote. So trying to resolve or make their issue better without a big addition or installation

hot_rod

could be as simple as deliming the coil Assuming the control settings are correct.

Larry Weingarten

Hi, That pattern could also be a crossover in the plumbing. Try shutting water off to the coil and opening a hot tap. It should stop running in seconds. If not, there is a crossover to find. 😈

Yours, Larry

bburd

You may need a low limit aquastat setting of 160 to 180° to get enough hot water out of that; the high limit needs to be set at least 20° higher.

That bypass or mixing valve is not up to code; it must be thermostatic and listed for the application to prevent water at full boiler temperature from getting to the taps, which is a scalding hazard. This will also go a long way to steadying the hot water supply temperature assuming everything else is working properly.

Deliming the coil may also be needed, depending on local water quality and age of the coil.

HVACNUT

Make sure the Economy setting is off in the Hydrostat. Limits at 180 High, 160 Low.

It should definitely have a thermostatic mixing valve.

Baths with a tankless coil need to be drawn slowly.

SuperTech

I would definitely make sure the aquastat settings are as @HVACNUT described. That's the first step. Next step would involve descaling the coil and adding a real thermostatic mixing valve. I prefer the mixing valve from Caleffi that has a thermometer built in to it.

If it was my boiler I would abandon the tankless coil and install an indirect water heater. My customers that have indirect water heaters never complain about running out of hot water or anything else. I can't say the same thing for my customers who have tankless water heaters, combi boilers and heat pump water heaters.

tcassano87

https://forum.heatinghelp.com/discussion/comment/1844913#Comment_1844913

so doing the same thing as descaling a high efficiency wall hung, flushing it out with vinegar?

tcassano87

https://forum.heatinghelp.com/discussion/comment/1844949#Comment_1844949

yeah Caleffi is my go too as well, good info to have about the setting son the aquastat. At least he will have the options of what he’s looking to spend verse what he’s going to get from the changes

psb75

I'll chime in the same as ethicalpaul the "hpdhw Evangelist". Put in a right-sized (50, 65, 80 gal.) heat pump water heater! It is a no brainer, especially with any still remaining incentives (from your electric co., state, federal etc.). Stop running the boiler in the warm months of the year! By the way, with the heat pump water heater you'll be using stand-by heat from the boiler to heat your water in the winter! How "cool" is that? ("cool" being the operative word. "Wink"). By the way, de-liming that coil set-up will not be so easy. No hook-ups!