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TL;DR: A recirculating pump for hot water was installed and is not working. Looking at the drawings an expansion tank and check valve were not installed. Does this explain why it's not functioning or is something else wrong?

As part of a renovation I had a circulating pump installed to get quicker hot water at the fourth story of our building. Prior to the renovation there was an existing water heater and hot water return line, but the hot water return line was capped a few feet from the water heater i.e. it was not installed.

We used an architect, licensed mechanical engineer, contractor, plumber, electrician. The mechanical engineer included the attached drawings for the system.

The pumps are now installed but there is no difference in how quickly we get hot water at the top floors. I took temperature measurements on the pipes which make me think that there is no flow in the hot water return pipe, because the hot water return pipe is cold 10ft from the pump. The pipe is hot close to the pump, but I think that is heat from the pump itself. The temperatures with one pump running are as follows (also shown on attached photo):

  1. Cold water inlet pipe ~10 ft from water heater: 73F
  2. Hot water pipe leaving water heater: 89F (note no hot taps were running upstairs while I took this measurement. When the hot water is running the temperature coming from the 1st floor faucet is 102F)
  3. Hot water return pipe ~10 ft from water heater: 75F i.e. approx same as the cold water pipe
  4. Hot water return pipe ~4ft from heater: 80F
  5. Hot water return pipe at aquastat: 91F
  6. Hot water return pipe next to pump: 111F
  7. Hot water return pipe where it joins cold water inlet for water heater: 88F

I confirmed that the pump in the foreground running, is set in the correct direction (i.e. pumping water towards the heater) and has both valves open.

Comparing the arrangement to the drawings I saw three differences:

  1. The aquastat is not wired to the pumps. This can't be relevant to the problem of no flow
  2. The drawings show an "Amtrol Therm-X-Trol" expansion tank which is not present
  3. The drawings show a check valve on the cold water line. As far as I can tell this check valve is not present

I've got two theories:

  • Theory A is that the water can't flow because without the expansion tank and check valve there is nowhere for it to go - i.e. the pump is trying to push water into the hot water tank, but the hot water tank is full so the pump just spins and heats up the adjacent pipes.
  • Theory B is that there is a blockage in the return line somewhere

I've turned off the pumps. Getting these installed has been a contentious process so before I start asking for this to be fixed I'd appreciate some help on to understand:

  1. Is the lack of expansion tank / check valve the only reason that the pumps aren't working as planned? Or is there likely something else going on?
  2. Should it be clear to a professional from these drawings that the expansion tank and check valve are new (vs existing)? I.e. is the engineer or electrician at fault for the expansion tank being omitted?
  3. Similarly to (b), is it clear from the drawings how the aquastat should be wired i.e. is the engineer or electrician at fault for the aquastat not being connected?

Pumps as installed Drawing 1 Drawing 2

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  • Is it possible that the existing, what you believe was a hot water return line, was actually not a return line but a stub out for something else ? That might explain why there is no circulating going on.
    – Kyle
    May 16 at 3:14
  • Yes you have to check if the loop is actually a loop. What happens on the other end on the 4 th floor?
    – bobflux
    May 16 at 5:59
  • The plumber told me it was tied in to new plumbing at the fourth storey bathroom but the walls are now closed up so I have no way to check.
    – jweob
    May 16 at 8:03
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    There are a few ways this could be broken, such as a failed pump, failed pump controls, incorrect piping, or an air lock (i.e. there isn't water at the pump). The lack of an expansion tank or check valve is unfortunate but unrelated. In any case the resolution is the same: call the professionals that just installed this system and have them fix it. And let us know what it was! May 16 at 17:33

1 Answer 1

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If you don't have a check valve near the pump, then there should be a thermostatic valve somewhere else far away. They are usually installed under a bathroom sink. That valve might be disabled or failed.

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