We've just had a our pressure regulator replaced, and a new recirculating pump installed. All 3 showers used to get hot water reasonably quickly (15-20 seconds). Now the shower furthest from the water heater won't heat up unless a shower or hot faucet in another bathroom is run. It just runs luke warm at best. The hot faucet in a sink in the same bathroom is the same - just luke warm, but no problem with flow rate.

What is stopping hot water reaching the shower, unless another bathroom's hot water is on? Doesn't sound like an air blockage, and it seems that water is still flowing in the shower through the hot pipe, because it gets colder when the temp control knob is turned to "cold". Weird and annoying!

  • Hello, and welcome to Home Improvement. Would you add a diagram of your piping and pumps? May 11, 2019 at 20:19
  • I would if I had the plans!! Water Heater (& recirculating pump) in garage on 1 side of 3500 sq ft single story. All 3 bedrooms on opposite side of house (shaped like 3 sides of a square) with master bath furthest from garage.
    – Marcus
    May 11, 2019 at 22:40

2 Answers 2


Here's the answer: The problem was solved when: 1) The recirculating pump was connected the right way round to suck water back to the water heater from the far side of the house AND... 2) The new digital timer was programmed correctly and left on AUTO not OFF....!

Still can't figure out why it got worse simply by replacing a non-functioning pump with a good one, that was turned off (taking 2 minutes instead of 15-30 secs). But as long as it's better now I don't really care!


If this is one of those "recirculate hot in the cold line" systems, rather than a dedicated recirculating return system, I suspect a check valve is not working. Might also be the case with a dedicated return line too, as those usually return to the bottom of the water heater where things are fairly cold.

So you get mixed hot and cold rather than just hot, as water flows from both the return line (or cold acting as a return) and the hot line.

Possibly the work caused some debris to get into a check valve. Possibly the old pump had a built-in check-valve and the new one does not.

  • When the hot faucets / showers etc were first turned on after new recirculating pump was installed, I saw several secs of "rusty" water at each tap. Presumably there is a dedicated recirculating return system. The water in it had not moved, prob. for 3 years!! Didn't know I had this pump, & it wasn't plugged into power. If there is "debris in a check valve", why do I get barely luke warm water from the hot tap/shower, but do get flow, but it won't get hot. However it flows hot within 30 seconds of turning on hot in another bathroom, (where hot water flows in 3-4 secs!)
    – Marcus
    May 12, 2019 at 18:05
  • So it turns out that the recirculating pump is a "sucker" not a "pumper"! And further it was installed the wrong way round. As a sucker, it was connected to the cold water side of the water heater, and when connected the wrong way around, instead of sucking cold water away from the farthest bathroom, it pumped lukewarm water from the bottom of the water heater to the bathroom. Hence it took a long time and seeming flow to other bathrooms to get hot water to the end of the line! Now it's the right way around it works. Hot water in a few seconds.....
    – Marcus
    May 14, 2019 at 23:22
  • Write that up as an answer. It's perfectly fine to answer your own question on here....
    – Ecnerwal
    May 14, 2019 at 23:29
  • Famous last words - there was hot water in a few seconds when the plumber was here. But not since. Been away so couldn't deal with it until now. It takes over 2 minutes to get hot water to the far shower and the time is the same whether the recirculating pump is on or off..... Sounds like this "check valve" issue is on point!!
    – Marcus
    May 29, 2019 at 15:49

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