Tap water is too hot

Markus2

This issue gradually got worse over a couple of years. I have a System 2000 with a heat ex-changer and a indirect storage tank. I replaced the storage tank thermostat but the water still gets too hot. The circulator pump is a Taco 006 model. It is receiving the proper voltage. Any help would be appreciated. Thanks!

Ironman

What aquastat did you use? If it has three terminals, you could have a wire misplaced which would also cause it to overheat.

Code requires an ASME 1070 approved tempering valve to prevent what you're experiencing.

EBEBRATT-Ed

If the indirect is on it's own zone with a pump you might have a flow check valve that is leaking by

Markus2

The aquastat is a 2-terminal and is functioning properly. In looking into this a little further, it seems like the circulator pump is circulating the water very slowly. I didn't realize this pump had an internal check valve. Maybe it's restricted? I'll have to take this apart and see.

hot_rod

I think Ed is correct, you may have ghost flow to the HX when it is in heating mode. That could cause a slow creep in DHW temperature.
You could disconnect the aqua stat wire and see if temperature creeps without any HW call.

It is good practice to install a listed thermostatic mix valve join ALL DHW systems. Several states now require that even on tankless.

The tankless WH companies are pushing for a new standard that would allow the tankless to be the accurate, listed temperature control and eliminate the mix valves. It is a tight standard to meet + or - a few degrees and accurate response within a few seconds to temperature change.

HVACNUT

Is the thermostat wired to the top left terminal of the manager?
Is the domestic side of the flat plate heat exchanger hot when the 005 is NOT running?
Is the 005 always running?
What temperature is the thermostat set for?

Markus2

Yes, it's wired to the top left of the manager.
No, the exchanger is not hot when the 006 isn't running.
No, the 006 is not always running. Only when there is a call for heat and about 5 minutes afterwards.
The thermostat is set for 120 deg F.
BTW... I had mistakenly originally posted that I have a 005 but it's actually a TACO 006.
Thanks for your helpful questions.

Alan Welch

How old is storage tank? Might be the dip tube failed and hot water is not getting sent to bottom of tank.

Jim Hankinson

Generally when you have this situation it's due to a flow restriction in the domestic side of the plate heat exchanger. The slower the flow, the hotter the water going into the tank. With the system operating to make hot water, open a fixture and put your hand on the pipe connected from the domestic out of the PE to the cold tapping on top of the tank. If you can't hold your hand on it there's a flow issue.

The dip tube is only 20" long and is seldom an issue.

The PE can be removed after isolating the heating system and the domestic and cleaned with a de-scaler such as CLR or a citrus based cleaner.

Condoman

Make sure non of the zone valves are manually overridden. That is what I had when the same problem occurred. Service tech forgot to reset it.

Markus2

The storage tank is 7 years old.
Jim, I tend to agree with you about the flow restriction. I can not keep my hand on the pipe as it's very hot. The hot water tank occasionally spits out water due to the high temperature. The water coming back to the circulator (Taco 006) is not warm at all. I have experimented and flushed water through the domestic side of the heat exchanger and there are no restrictions whatsoever. Could it be the impeller of the circulator or the circulator's internal flow check?

Alan Welch

There should be a way to backflush the heat exchanger, have you tried that. Pictures of the piping at circulator would help.

Markus2

Yes, I did backflush the heat exchanger and it was fine.

Jim Hankinson

Yes, it could be the IFC. Possibly the impeller but not too likely

HVACNUT

Agree with Jim. Seems like the IFC is stuck open.
Do you have the problem in summer when there are no space heat calls?
You can replace the IFC only. No need for a new circ. If the impeller was bad you'd have no hot water.

Markus2

Yes, the problem exists throughout the seasons.

HVACNUT

> @Markus2 said:
> Yes, the problem exists throughout the seasons.

There you go. Replace the flow check.

hot_rod

Is that one of those funky Taco circs with the check in the suction side, that long volute bump out? Are those checks replaceable?

Markus2

I replaced the Taco 006 cartridge, IFC (check valve) and the thermostat and I still get excessive hot water. I really enjoy troubleshooting but this has me baffled. I still feel like there is some kind of restriction to/from the DHW storage tank.

Alan Welch

How did you back flush the plate exchanger ? Is this town or well water, and what size is the tank?

HVACNUT

According to the EK Tech Manual, these are the items to check in a "water too hot" situation.
Does the burner light turn on and off, with short cycling of the burner?

1- Domestic circ not running.
2- Defective check valve.
3- Back flush heat exchanger.
To properly Backflush (see attachment), close ball valve A and open Backflush valve B. Should get a good flow of water, possibly with some debris. If flow is slow, replace the heat exchanger.
4- Air blockage. If the "domestic out" piping is overhead at the ceiling level, or has a long run, it may be airbound and the domestic circ is not able to push the air into the tank. This would normally occur only during start up or if a part was replaced and the air was not completely purged. Backflush to purge air.
5- Add scale stopper - Add an EK scale stopper to the cold water supply line feeding the tank.

EK Tech Support : 1-800-323-2066

EK part numbers:
10-0416- plate heat exchanger for EK1.
10-0435- plate heat exchanger for EK2.
10-0650- Scale stopper
10-0650-C- scale stopper replacement cartridge for scale stopper.

Markus2

I initially back flushed the heat exchanger with too low of flow and not for very long. It is town water. Today I once again back flushed the heat exchanger for a longer period of time and verified that it has very good flow. The tank holds 40 gallons. Thank you for all the helpful information.

Alan Welch

Did you close the valve under the circulator first, and what did it look like when it came out?

hot_rod

If you suspect the HX is limed up on the DHW side, you will need to circulate an acid cleaner. Backlashing alone will not remove scale build up.

Buy a tankless WH descaling kit.

Markus2

Yes, I closed the valve under the circulator before back flushing. The water came out clean and normal looking. Today I took some temperature readings of the copper pipes. The one temperature reading I am a little concerned with is the temperature of the water coming back to the circulator. It barely gets warm if at all. Is that normal? The temperature going into the DHW tank got as high as 170 degF.

hot_rod

#1 on HVACNUT list above, is the circulator running and actually moving flow?

Some brands of circulators have a screw in the back of the motor that can be removed to see if the pump is actually spinning.

In your case, if there is power to the circulator and no flow, either an air lock or failed (stuck, burned out) circ. You may need to remove it to see what's up.

Alan Welch

If the circulator wasn't working he wouldn't have enough hot water. His problem is it's too hot. 170 degrees out of the plate exchanger doesn't seem unreasonable, it seems like it isn't mixing in the tank, that's why I suggested the dip tube may be bad, and the hot water is stacking at the top instead of being forced down and mixing with the cooler water.

Jim Hankinson

The temp of the water going to the top of the tank should be 135-140 during a HW cycle. It sounds like a restriction in the PE. Try removing it and cleaning it with CLR or other descaler. Have a Scale Stopper installed to prevent future buildup.

If the circ was not running there would be no hot water.

Markus2

Alan, I don't know how often the dip tube is an issue but it sure seems to be very plausible. I agree with you and also feel that the water isn't mixing properly within the tank. All other components have been verified to be good and the water flows very well through all the piping. If it is in fact the dip tube, does the entire tank have to be replaced? Thanks again!

Alan Welch

I would first either do as Jim suggested, or have the installer check it out..

Markus2

After replacing the Taco pump cartridge I could feel roughness when I would spin the impeller by hand. It was as if it had a bad bearing. I also back flushed the heat exchanger and I no longer have a "domestic hot water overheating issue". Thank you all for taking the time in helping out!