Insufficient Hot Water

Written on: November 6, 2012 by Wayne Lawrence

Last month I wrote of how important water pressure checks are in our diagnostic troubleshooting procedures. By now, as you are reading this, nature has again provided us with more work, for this time of year the inlet water temperature is cooler. This results in many insufficient hot water calls as well as thermally shocked, leaking water heaters.
I’m sure most in the field are very aware of all that follows, but in case we have a few new readers onboard, I’ll go over a few of the basics. The first and most important thing to do on these calls is the service detective interview of the complainants! There is a huge difference between “insufficient temperature” and “insufficient hot water duration” even if, sometimes, it can appear to the customer that they’re exactly the same thing!
Key questions to ask would be how long are they living in the home, and when the problem first became noticeable? If the problem has become more apparent now that the weather has changed, that is a huge clue as to the direction in which to look for the resolution. If they just moved into the home, a complete check of the system will be in order. Ask how many are in the home, if there has been a recent remodel or a Jacuzzi tub added, if there is a car wash sized shower head, and if the problem happens to be in only one fixture—usually a shower body. It could be that the adjustment is off or the thermal element needs to be replaced.
I have encountered a mixing valve located away from the heating appliances, which caused much grief until it was found! Of course, the street pressure must always be checked! Oh, you checked it already? Great! Glad you read October’s article! In that case, now we’ll discuss tankless coils, aqua-boosters, indirect- and direct-fired water heaters
Tankless coils: Job security #1! I’m amazed at how many tankless coil calls I go back on! First consideration on the list—it had better have a mixing valve on
it, because it is required by code and because we are professionals, we should notice these details when inspecting these systems. If not, I hope the customer was informed of the scald hazard, has received a well written, quoted estimate to have one installed, and if declined, a notation that it was declined by the customer on the legibly written copy.
It should be clearly written that the customer was informed of “a potential scald hazard, and that the repair was declined at this time.” The customer should have been asked to sign the copy of the ticket that goes back to the office. I also make a copy for myself. I have seen in the past, especially around the holidays, a guest getting burned, usually while washing their hands. Often, the customer wants reimbursement for the emergency room visit! If that’s all that happened, you got off easy!
I shouldn’t even have to mention what could occur if a child, with their face at sink level, opened the hot faucet full blast! These preventable accidents happen all too often! These calls usually go like this: The water sitting in the coil is 180-190°; they open the fixture, get a blast of scalding water, and then it goes lukewarm, and sometimes, even goes cold. I’ve been on too many calls where the tech just simply raised the aquastat to compensate for the lack of duration, and left only to have the customer call back for the same problem! On these calls I also pull the aquastat to make sure the sensing element is all the way into the well.
I do not like to see ball valves on the coil piping, since there is no restriction, and if the water pressure is over 60 psi, the water is flowing through the coil too fast to pick up heat. A non-producing coil condition will show up quickly. Have the customer open a fixture to draw hot water only, and the domestic water temperature will cool before the boiler will even restart. That will show poor heat transfer, and the coil will need to be cleaned. You can try the coil boil and/ or bounce and flush method, or just have the coil cleaned. If there is a mixing valve, make sure the valve works and the water is not short circuiting through the valve. I try to keep things generic in my articles, but I try to sell a thermostatic mixing valve whenever possible.
Aqua-boosters: The most common insufficient hot water call I get on these is the booster circulator located on the outlet side of the tankless coil, which can cause premature failure of the circulator’s impeller due to cavitation. I like to pull the water from the aqua-booster tank, and push the water through the coil with the circulator. There should be a check valve to keep water from short circuiting through the booster tank and directing the inlet water through the coil, and then into the heater each time the fixture is opened. As with direct fired water heaters, the dip tube should be checked whenever there is an insufficient duration call. On these calls, if the aqua-booster circulator is running, the boiler will drop temperature and the burner will start. If the boiler temperature isn’t dropping, the circulator may be running—but the impeller is gone! I’ve gone back on so many with missing impellers! Hint! Hint!
Indirect Water Heaters: Job security #2! There are lots of things to look for here. First on the list is to make sure the boiler is able to, or is fired to handle the connected load. In most cases, the indirect needs more Btus to recover than the entire house needs for heat on the design temperature coldest day! Second, check to make sure the indirect is piped to manufacturer’s instructions using the required pipe sizes, and the circulator is sized with the correct head and flow capability. I often see many with undersized piping, and if piped using zone valves that are not “full port” valves, there is now a flow restriction resulting in longer recovery times. I like the indirect water heaters wired with priority whenever possible to shorten the recovery time. The key here, again, is if the indirect water heater’s circulator is running, the boiler temperature will drop. If the indirect heater’s coil is dirty, there goes the heat transfer!
Direct fired water heaters: There are a few things I look for here when I get an insufficient hot water duration call. The first, is the heater too small for the demand? I’ve seen customers expecting to fill an 80-100 gallon Jacuzzi bath with a 30 gallon direct fired water heater on a 15 degree day! Of course, the firing rate is always checked, and I do not like finding direct fired water heaters “down fired.”
The next thing I got into the habit of checking is to pull the aquastat or electronic temperature control and make sure the sensing element is all the way into the well. Air is a poor conductor of heat and there may be too long a lag before the burner restarts, in which case recovery will suffer. The last thing I’ll mention here is the dip tube. This is an easy check, since speaking with the complainant will send you in the right direction. This problem shows the same symptoms as what happens when a tankless coil isn’t producing. The water will come out hot, but the temperature will drop quickly, and the burner will be slow to restart. When the dip tube is missing, the water will short circuit at the top of the heater.
Well that’s it for now, as the 12-hour days in the van are catching up to me, and the magazine deadline is calling! Next month, we’ll go over a few more indirect water heater job security issues, and how to clean and flush the indirect heater’s internal coil!
Stay safe, Wayne