Tom Sahagian in Bricks & Bucks on July 17, 2019
When my friend Bob and his wife found out they were going to become parents, they moved to a larger apartment and sublet their small condo unit in a prewar Brooklyn building. All was well until very recently. Then suddenly their tenant threatened to break the sublet because the domestic hot water (DHW) in the condo had gone completely haywire.
Hot water would take forever to arrive, or it would come and go, or not arrive at all. And the problem seemed to be building-wide. The condo board brought in a plumber to assess the situation. His solution was to replace the recirculating pump as well as the check valve on each return line. (Check valves allow water to flow in only one direction.) This fix seemed wrong to Bob, so he called me in for a second opinion.
I was immediately skeptical because the DHW system had worked pretty well before it went crazy. The key was to find out what had changed within the system, and when, and why.
Easier said than done! As is often the case, there was a lot of conflicting information. One apartment claimed that water would come out of the showerhead for a minute or two and then stop altogether. No one was quite sure when the problems had started, or when various recent plumbing work had been done, or if the work was relevant to the DHW system. I decided a site visit was needed.
The DHW system in most multifamily buildings in New York City includes a small pump and a network of recirculating lines, which keep hot water moving constantly through the system. The pump is supposed to run 24/7 so that there is always hot water close to the faucets and showers in every apartment; this way, people on the upper floors don’t have to wait for hot water to travel all the way from the basement.
The plumber seemed to be saying that one or more check valves were missing, but if that had been the case, the system would have acted up a long time ago. Even if he was saying that the existing check valves had failed, it’s a bit unusual, and for all the check valves and the recirculating pump to fail at the same time would be rarer still. I entered the boiler room and noticed a few things right away: a new DHW mixing valve had recently been installed, and the recirculating pump was controlled by a snazzy new digital aquastat.
An aquastat governs when the recirculating pump is turned on or off. But in most systems, like this one, that have a mixing valve, the recirculating pump must run virtually 24/7 to control the water temperature properly. I wrote down the aquastat’s on and off setpoints – and began scratching my head. Something wasn’t right, but I still didn’t know what.
Looking more closely at the recirculating pump, I noticed that the exterior appeared to be in very good condition, and the bolts connecting the pump to the pipe were shiny and brand new. Yet the recirculating pump clearly was not operating. This was making less and less sense by the minute.
Then it hit me – the aquastat setpoints were backwards, so that the pump would never turn on! I quickly reversed the setpoints, and the pump started up immediately. There was no need for new check valves or a new recirculating pump. The plumber’s $680 “solution” was a waste of money.
This was a classic case of someone charging a lot of money for an unnecessary “fix” when the real fix is a minor, inexpensive item. The contractor installs the expensive stuff, makes the real fix more or less on the sly, and then says “See? You needed a new (expensive unnecessary thing).” Happens all the time. To avoid this problem, co-op and condo boards should get a second opinion – preferably from someone who actually knows what they’re talking about.
Tom Sahagian is a writer, teacher, and consultant on energy efficiency.
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