I’m putting this in IMHO (though it will have a factual answer) because I think it invites speculation.
Last week we visited friends in Texas & I did some work around the house for them. One thing they didn’t ask me to do, but that I spent quite a lot of time puzzling over, was figure out what’s up with their water heating.
The setup: the house is 4,000 sf. It has two water heaters connected serially in the attic, both set to the same temp, feeding three showers on the ground floor and one on the second floor, plus the usual faucets. It’s propane-fed.
One of the ground floor showers heats instantly, as does the faucet in that bathroom. Two of them not only don’t heat instantly, but in one you have to run the tap + the shower for a good 10 minutes to get hot water, in the other at least five minutes.
I stood in the attic and had them turn on each shower, and what sounded like water flow did kick on instantly for the ‘hot’ bathroom and not the others, but since all of them eventually do heat, I may be reading too much into that.
Eventually she’ll get a plumber, but they’re expensive and difficult to schedule, and frankly the whole thing confused me.
When you say “connected serially”, do you you mean that the outflow of one water heater goes to the inflow of the other? Is it like this?
Outside cold water —> [Heater #1] —> [Heater #2] → Hot line for house
It could be that the lines for the two bad showers take a much longer path than the good shower. It may take that many minutes for the hot water to make it to the bathroom. Although it does seem like that’s a long time.
One possibility is that the two bad showers have a failing anti-scalding valve. That’s a valve that helps prevent the water from getting too hot. It may be putting too much cold water into the stream at first. One test might be to see how long it takes for the showers to get warm when the handle is in the middle. So rather than putting it all towards hot, put the handle in the middle so both cold and hot water is coming to the shower. If the bad showers get warm faster with the handle in the middle rather than all hot, it might be the anti-scalding valve.
10 minutes is way too long, and it used to work fine. It’s also affecting the taps, but if they have valves they might be at the bathroom level - I’ll make that suggestion to them! Thank you.
If any of the bad bathrooms have a sink or tub with dedicated dials for hot and cold, try that with just the hot water. The taps which are just for hot or cold should be connected directly to the hot or cold lines without any kind of mixing valve in the path. If a dedicated hot tap gets hot quickly but the shower takes a long time, then that would be a sign of a bad anti-scald valve.
You mention there was instant hot water in the first floor the bathroom. This informs me there is probably a circulating pump in the system to enable instant hot water since the water heaters are in the attic. On the other baths with the 10 minute delay, I can only imagine its plumbing is somehow separate from the other bath or it either has no circulating pump or it has failed. If these baths are closer to the water heaters, I cannot explain a 5 to10 minute delay.
To add to that, a quick way to check for this is to turn on one of the problem showers and wait for it to get hot. Then go around the house and, without turning anything else on, feel hot water supply line leading to each (single handle) faucet/shower. It shouldn’t be cold. If you find one that’s cold, that means cold water is moving through the faucet and into the hot water side, causing the problem. That’s the faucet that needs to be repaired. You can prove this by shutting off the hot and cold water lines leading to that faucet and doing the test again.
Also, it should be noted, that this test is easier if the water in the house hasn’t been run for a while and all the pipes are at, or close to, room temperature.
This suggests that there’s something restricting hot water supply to the other bathrooms.
Turn off the cold water to one of the bad bathroom taps and turn it on full. This should tell you if there is adequate hot water moving towards that bathroom.
I once had a serious problem with low water pressure in the whole house. Turns out I had turned off the supply for some reason or another and when I reopened it, I didn’t quite open it all the way. Perhaps someone fiddled with a valve on the hot water line that goes only to those bathrooms.
Is it actually, literally, 10 minutes? Measured? That’s insane. It’s can’t just be a pipe issue then, using this Pipe Volume Calculator , assuming 1.5 gal/minute for a low flow head and a 1” pipe, (which is actually too big), that means 370 feet of pipe between the heater and the bathroom. With a more typical 3/4” pipe it’s 650 ft. That’s 3 Stooges level of bad plumbing.
Yes, 10 minutes, measured. She’ll get a plumber in, but this is our friend who’s recently widowed and who has minimal income, so I try to help her with stuff. This one is beyond me, however.
To be clear again, it didn’t use to be that way…but it has gone on for a while, so they just live around it and use the other showers.
In the same vein as the suggestions about looking for a problem with an anti-scald device, it could also be the mixer cartridge in a single-handle faucet. I had one recently fail in a shower. The first symptom was cold water from some faucets would come out tepid at first before transitioning to cold. The timing corresponded to the central heating running more in fall, so I assumed it was water pipes running adjacent to air conduits. But then I was draining my water heater, and I could hear water running into the tank from the hot water side.
Maybe you have a cartridge failing downstream from the one shower that’s working. The water could take a long time to heat up because cold water is intruding in the hot line.
I’m sure she’s dealing with a lot, but it might be time to start thinking about moving into a more manageable place. “Strange pluming problem” is just one of many creative ways a 4,000 sf. house will eat up all of her minimal income. Get this problem fixed and then get out before “strange electrical problem” has a chance to pop up.
I agree with Dereknocue67 that there’s probably a recirculator pump (or two) that has failed. Usually that’s in the mechanical room by the water heater, but it could also be in a cabinet under a sink.
To test if it’s a bad mixer, turn off the cold water valve to all the sinks in the house which have a mixing cartridge no matter where they are, like the kitchen, all bathrooms, powder room, etc. Then turn on the hot water in the bad shower and see if it still takes 10 minutes. If it heats up quickly, then that would point to one of the sink mixing valves is bad and is allowing cold water into the hot water line.