Not enough hot water in shower

Discussion in 'Shower & Bathtub Forum & Blog' started by Doug1225, Feb 13, 2019.

  1. Doug1225

    Doug1225 New Member

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    Location:
    Cotuit, MA
    We have tankless hot water with oil fired furnace. In December, we had the annual check up for the furnace. There was a problem, they replaced the aquastat as the water in the boiler was getting too hot, he then purged the system and said all was good. Since then, we have a problem with not getting enough hot water in the upstairs shower. We also have a shower on the first floor, it has plenty of hot water and all sinks provide hot water. Also, replaced the diverter valve in the Temptrol shower unit that I am speaking about and that didn't help either. Also, the tub spout only gives lukewarm water, never hot. Do you have any idea what the problem could be? Hope someone can help us.............
     
  2. Dana

    Dana In the trades

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    Terminology: In the HVAC world "furnace" refers to heat delivered by hot air (ducted or ductless). What you have is always refert to as a "boiler", not furnace- the terms are not interchangable.

    Low water heating performance from embedded tankless coils in boilers tends to be closer to the rule than the exception. It may very well be that the new aquastat was set lower than what it takes to get adequate hot water performance, whereas the hot water performance was adequate back when the boiler temp was ...getting too hot...".

    Before boosting the boiler temp, see if you can't fix it at the shower end. The fact that the problem seems to be limited to just one shower points to the shower mixer (which is not the diverter). Most mixers have an adjustment screw to limit the maximum amount of hot water that can be mixed in. The Symmons mixers aren't all identical but they're pretty similar, see if you can't just get there by adjusting the hot water limit screw. If that doesn't do it, try raising the water temperature.

    MA code for new installations requires a thermostatic mixing valve or tempering valve on the output of the water heater (any type), and the installer is required to set it to something like 115F (I'd have to look it up again to get the exact temp) for distribution to sinks and bathing taps, but dishwashers and laundry is allowed untempered water. If your tankless coil has a tempering valve on the output, turning up the temperature there is the first step.

    If that fails or you don't have a you may have to bump the boiler's temp to see if it makes the difference. Raising the temperature of the aquastat (particularly the low-limit) will improve hot water performance, but before you just crank on it, what are the current aquastat settings?

    There may also be an issue with the anti-scald valve (if you have one.) The Temptrol series has an internal anti-scald valve. If that is sticking or if there is a lot more pressure on the cold side than the hot, that may be limiting the hot water flow too.
     
    Last edited: Feb 13, 2019
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  4. Doug1225

    Doug1225 New Member

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  5. Doug1225

    Doug1225 New Member

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    Sorry for saying furnace, it is a boiler. The aquastat is set at 170-190, so can we boost that? Have adjusted the set screw in the past, should I do it again? Should I buy all new guts for the Temptrol? We have a new Taco mixing valve but does not give a temp, I have included pictures with mixing valve to the left and aquastat to the right in the photos. This is so frustraing. I can do a lot of DIY but I'm not a plumber.
     

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  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The mixing valve is usually set for 120-degrees, as that's the maximum code wants to most things in a home. If you have a good thermometer, run water until it is full hot at say a sink, then fill up a glass while water is still streaming into it and measure the temperature. This is easier with an instant read one, but any one that can read high enough will work. If the mixing valve is low, crank it up some, but do not exceed 120-degrees.
     
  7. Dana

    Dana In the trades

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    Try ADJUSTING the hot water set screw on the Temptrol first- that's almost certainly the issue.

    The new thermostatic mixing valve is most likely the reason the hot water performance dropped in that shower, but don't adjust it up until you've maxed out the range on the Temptrol set screw.

    With the low-limit on the boiler set to 170F that isn't likely to be the limiting factor here (it might be, were it set to 140F or something). The mixing valve sets the temperture of the water entering the hot water distribution plumbing no matter how high you set the aquastat.
     
  8. Doug1225

    Doug1225 New Member

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    the water at the sink is reading 117, so guess that's good. Will try adjusting the set screw next, will let you know the result, thanks
     
  9. Doug1225

    Doug1225 New Member

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    If we decide to add a new hot water unit, either tankless or stand up, is this possible with a tankless system in place now? Can you disconnect the old tankless unit?
     
  10. Dana

    Dana In the trades

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    Yes, you can disconnect the tankless, set up an indirect-fired tank operating as the "priority zone" off the boiler, and lower the low-limit on the boiler to 140F for an oil burner. There is a MassSave rebate of $400 for switching from a tankless coil to an indirect from a for either oil or gas , and a $700 rebate for a gas tankless. An indirect will be more efficient overall annually than a non-condensing standalone tank, but not a condensing gas tank or gas tankless. Unless it's a very small boiler you'll get more satisfactory hot water performance out of an indirect than a gas tankless, especially when it comes to filling tubs.

    The installation cost of a tankless can be pretty severe, since it may require upgrading the gas supply to your house, and will always require a right-sized dedicated gas line tapping in very near the meter/regulator and the tankless, not branching off from another line. In MA a 2 bathroom home would need at least a 180,000 BTU/hr burner on a tankless to have any margin to cover other uses during two simultaneous low-flow showers.

    When installing an indirect to a cast iron boiler it's worth installing a heat purging economizer control such as an Intellicon HW+ or Hydrostat 3250 Plus. You will probably never need 190F water to actually heat the place, but it's likely you needed 170F water for reasonable hot water performance out of a tankless coil in winter. The higher standby and operating temperature increases the standby losses, and the short 20F swing between 170F and 190F under-utilizes the thermal mass in the system, resulting in shorter, less efficient and more frequent burns. The smarter boiler controls will optimize use of the thermal mass, and lower the standby losses. In your case it will likely be on the order of 15% lower fuel use, maybe even better than that. Most gas boiler can be cold-started, which would even further reduce standby losses during the shoulder seasons and summer.

    There are no electric tankless water heaters suitable for MA type incoming water temperatures, but an electric heat pump water heater is cheaper to operate than an oil fired indirect, though at the moment there are no incentives for fuel switching. A heat pump water heater installed in the boiler room would "harvest" the standby and distribution heat loss to the boiler room in winter lowering the room temperature a couple of degrees which, lowers the net heat loss from the house, and dehumidifies the boiler room in summer, converting the latent heat of vaporization into sensible heat inside the insulated tank. Even without any MassSave rebates for doing that it might still be a better way to go, especially if you normally run a dehumidifier during the summer.

    Longer term it looks like policy makers in MA are working toward moving away from oil heat, and is likely to ramp up the subsidies for converting to heat pumps. Cold climate ductless heat pumps are quite a bit cheaper to operate than the typical 3x oversized oil burner. (Yours is probably at least that oversized for the space heating load simply to be able to deliver reasonable hot water service from the tankless coil.) I can go into that in greater detail if you're interested. Right now MassSave will kick back $1600/ton for cold climate ductless heat pumps that are displacing oil heat. These things also deliver extremely quiet extremely efficient cooling as well. The installed cost (pre rebate) is usually between $3.5 - $4K/ton in competitive bidding. A 3/4 ton Fujitsu 9RLS3H will deliver 15000 BTU/hr @ +5F which is almost half the design heat load of my sub code ~2400' antique house (+1600' basement) at +5F, and usually installs for about $3000 (pre-rebate) in competitive bidding.
     
  11. Doug1225

    Doug1225 New Member

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    Thanks for that info. I adjusted the set screw, doesn't seem to be any different. Is there any other solutions that you can suggest? Should I buy new guts for the Temptrol or a whole new unit, maybe a different brand? All suggestions are welcome, thanks.
     
  12. Dana

    Dana In the trades

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    If the water at the sink is 117F you should be able to get at least 110F out of the shower mixer. Bumping up the temp at the new mixing valve at the boiler another 5F might get you there without huge scald risk. If that isn't enough, rebuild/replace the Temptrol. It's possible that the anti-scald valve is sticking or is too sensitive to pressure differences between the hot and cold side.
     
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
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    New England
    All modern shower valves have a means to limit the maximum hot mix to the shower head. If you haven't already adjusted that, try that. Depending on the brand, the exact method differs some. But, keep in mind, it's the middle of winter, and the ground water is cold, so it takes more hot in the mix to get a hot shower. Come summer, if you adjust it for good temps now, it will let it get too hot then. This is one reason why I prefer a thermostatically controlled valve...it adjusts itself...you just set your desired temp, and if there's enough hot water, it will adjust the mix, summer/winter. I put a link in the tutorial section that shows how to adjust some of the more common shower valves' limit controls.
     
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