Owners just moved in to their new remodel. Complete replacement of plumbing systems included. Installed a new Bosch 250 SX on demand hot water heater as part of plumbing. The Bosch unit apparently working normally, heats up fine, no error codes on display, etc. Problem is that at kitchen sink, bathroom sink, when hot water is turned on it gets warm right away (few seconds delay) but not hot. As it runs the water gets hot after about 90 seconds then turns cold, even as the Bosch unit continues to run, and hot water doesn’t recover.
More info: Water pressure into house from street is 82 psi, a little high. Trouble shooting guide with Bosch says that if hot water fluctuates it could be that water pressure is too high. In this case the heater itself acts as a flow restrictor while there is nothing comparable to restrict the cold water. Solution suggested is to install a pressure reducing valve where water enters house. The apparent idea being that if there is not such a large discrepancy between hot and cold pressures, the cold will not overpower the hot at the faucet.
Note: in the shower, which has a pressure balancing valve, this problem does not exist giving credence to this theory. Only unbalanced valves have this problem. I spoke with the local distributor about this and he agreed that is where he would start.
So, two days ago, we installed the pressure reducing valve, factory set at 50 psi. Problem still exists, although mabye slightly better. the Owner wasn’t sure. There is a noticible drop in water pressure, though.
Any ideas on where to go from here. I will be talking to the plumber this week also, but I wanted to see if anyone had any ideas here as well.
Thanks in advance for any insight.
Brad
Replies
I suspect something loose in the lines/valves for the hot water that is restricting the flow.
Try disconnecting the lines and blowing them backwards.
i will try. but, it would seem like a long-shot coincidence for that to happen in two valves at the same time, wouldn't it? or are you thinking a blockage in the hot water line at the heater and not at the individual faucet valves?
It is, but think that it is possible, but not knowing the layout I was thinking of some path that is common.I don't think that putting the PRV in the cold side only will work and I don't think that follows the symptoms.When you first turn on the faucet, I am assuming that it is at some intermediate setting, part hot, part cold, within a 2nd the pressure has equalized on the branches and you are getting a set flow which is some ratio of the hot and cold. Either one of 2 things is happening. Either the flow of the hot water is stopped/reduced or the WH is stopping to make hot water becaue the flow is too low.How you did not report any reduction in flow and a something stopping the hot water line would some affect on flow.Here are some test that you can do.!. When this happens start feeling the lines and find out which is hot and which is cold and where the hot stops. You might have a cross flow through the shower pressure balance (don't know if that is possilbe) or some other place.2. Turn the faucet to full hot. What happens? Do you a small flow (indicating a restrution) or full flow of hot (indicating a pressure problem) or still cold/cool water (indicating some cross flow connection).3. Leave the faucet alone, but use the stop valve to close off the cold water side. What happens?4. Turn on another faucet, full flow hot, to make sure that the water heater has enough flow to keep it triggered.
thanks for the tips. as to your post point 1. the only valve in the house that is a pressure balance valve is the shower and that is the only one that works correctly. so, i wouldn't expect there to be a problem with cross flow in that valve (if i understand you correctly)2. when i turn either the kitchen faucet or the bathroom sink faucet to full hot (both single handle faucets) the water flow drops a little and that is when the water runs warm, then goes cold -- with the handle turned to full hot. as you are suggesting it seems that it might be a case of the heater not having enough draw to keep the unit heating. i didn't think of that.3. tomorrow i will try closing the cold side to see what happens.4. i will also try running mulitple hot sinks to see if that triggers a greater flow and see what effect that has.is there a way to adjust an on demand heater to trigger and maintain at a lower flow rate? or are they pre-set to a permanent trigger point?thanks for the help.brad
Here is an update. I didn't get a chance to check in here yesterday.I checked the filter screen at the hot water heater to see if it was clogged and reducing flow. It was clean.I turned off the supply to the water heater, shutting down the hot side of the system, and then opened each faucet on the hot side to see if there was any crossflow somewhere in the system. No flow when I did this so I don't think there is any crossflow anywhere.The manual suggests that perhaps insufficient gas flow could be causing the heater to not burn at optimum efficiency. The line is 3/4", matching what is recommended in the specs and none of the other appliances are having any problems with supply.When I turn off the cold side at each faucet, there is no discernable difference in either pressure or performance.I tried opening multiple hot faucets to increase the draw and see what happens. Still no difference.However, I did notice this. The cold supply to the water heater is a 1" pipe. The inlet and outlet from the heater are 3/4". Then, the outlet from the heater returns again to a 1" line that does not reduce until somewhere further on in the system. Could it be that after choking the flow down to a 3/4" pipe and then trying to supply a 1" line that this process of going from small to big is messing with the delivery? The pressure is still very good at the faucets.Or do you have another idea?thanks,Brad
So if I understand this correctly, after the hot water at the sinks has run for over 90 seconds it stays cold from then on, and yet the Bosch is putting out hot water. I'm no plumber, but doesn't that mean the hot water is getting short circuited somehow before it gets to the sinks ? Is there some type of recirc loop piped into the system to keep the wait time for hot water down at distant locations ? (I can't see how that could possibly work with an on-demand system). If there is an independent shutoff for the shower hot and cold, try closing them both and see if the problem persists at the sinks. That would rule out some kind of malfunction of the shower mixing valve. Or did you do that already ?
"However, I did notice this. The cold supply to the water heater is a 1" pipe. The inlet and outlet from the heater are 3/4". Then, the outlet from the heater returns again to a 1" line that does not reduce until somewhere further on in the system. Could it be that after choking the flow down to a 3/4" pipe and then trying to supply a 1" line that this process of going from small to big is messing with the delivery?"No, at heavey demand then you will get a somewhat reduced flow rate, but you would need to have all faucets open before you would have a problem.Is there a "view port" on the WH so that you can see the flame when it is in operation. If so what does the flame do?Have you felt the pipes when this happens?There are two possibilities, either the WH is not making hot water or it is "going" someplace else (or mixed with cold). Either case feeling the pipe would give lot of information. More so if the can follow then the whole way. But if the pipe out of the WH is not hot then you know that it is not making hot water.Maybe a bad unit.And how are the gas connections made? I have not seen this type of system, but I understand that in some place a medium pressure system is used where there is a regulator at each appliance. In that is the case the regulator would be susepct.
Tankless & instahots restrict flow for them to work more efficiently.
You probably have a greater restriction in the HW system than the CW system.
That's why the shower valve doesn't have this problem.
Are your faucets single or double handle?
If single you can restrict the CW at the angle stop that should make the problem go away------( this is not a fix) just a way of finding out if the hot is restricted.
Installing a prv pressure reducing valve on the whole system doesn't fix it either it just knocks both systems down equally.
You could put the prv on the cold system downstream of the tee that serves the waterheater---- that would restrict the CW without restricting the HW
It's not the textbook way to fix it but it could work.
One last thing the flow restrictors might have been taken out of the faucets -----they don't work as a pressure balance valve, but they slow the flow down so the HW & CW have a chance to equalize with each other.
the faucets are single handle. i didn't think of that. i can partially close the cold just to see if that helps the problem. if it does, why couldn't i just leave the cold partially closed down at the stop? they are gate style stops, not ball-valves. could i just leave them partially closed down?
Gate valves are used for full open or full closed.
They shouldn't be used for throttling----- generates too much turbulance & wears parts out.
Try some of the things Bill & myself have said & see what happens.
Then lets go from there.
i'll try that and let you know tomorrow.brad
If you installed a pressure reducing valve, you may need a potable water expansion tank. Otherwise when the water heats up the pressure in the pipes will increase on the house side of the prv.
Thanks, got this one covered. The plumber already installed the expansion tank.