I’ve posted this question over in plumbing.com, too. But I’m really stumped.
I have a Bosch tankless hot water heater that can’t get the water hot enough. This was a sudden development after tying in a new gas line to a dryer.
I am absolutely certain that my gas supply and pressure coming into the heater are correct. But pressure seems to drop after the water heater’s regulator.
I’d like to know how to test the regulator. I think I can even by-pass it since the line’s pressure is exactly what the water heater requires.
Replies
Hey,
What else is on that line? And, pipe size?
skipj
3/4 black pipe to the heater from the outside-the-house regulator1/2 to the dryerthere's a short line off the 3/4 to a stove, tooAfter much conversation with Bosch, I'm going to rebuild the water valve. The two work in tandem. Will let you know if that helps.
I like USAnigel's point though. Could be some pipe dope got in there?
K
How long is the pipe run?
My tankless tops out at 190,000 btus, which on a longer run, a little less than 40', needed 1" pipe at the beginning of the run. Even with only a range upstream."Research is what I'm doing when I don't know what I'm doing..."
There is usually a test port on the heater manifold. Measure the gas line pressure at this port when the heater is running at full load. You may find it drops considerably from the static pressure. Remember that gas lines sized for a tank heater may be too small for the BTU output of a tankless.
I had a similar problem and the pressure drop was caused by a 20 year old gas meter that couldn't regulate under the high flow rate from the tankless heater. After the gas company replaced the meter, the problem went away.
Being as this suddenly happened after some work on the pipes. I would look at the pipes to see if there is a blockage feeding the water heater. Check all the valves and flexes too.
Pressure is not enought, you need enought gas flow too.
Exactly, check the screen on the gas valve inlet, might have gotten some particals in it! Test the pressure at the regulator with the unit running.
I rebuilt the water valve. This did the trick, the burner flames are leaping up as they should. I think the temp. is still a bit lower than what I used to have, but I haven't had much chance to use the hot water yet.Everyone's advice about the gas line was certainly a good idea, but I think it was coincidence that the failure of the water valve happened just when I was tapping into the gas line.I'm not sure what the relationship between gas/water is, but certainly if the water is not flowing through correctly it's limiting gas flow.
Well done in getting it fixed. Extra well done in letting us know what the problem was.
I would still check the gas valve/filter at this stage.
I would think gas flow is reduced at low water flow to make sure the unit does not over heat.
Basicly your making a metal box very hot and trying to keep it cool with incoming water, not enought cooling and it melts or over heats.
Well, the hot water was with us briefly. Three showers, a load of dishes, and a couple spins of the washing machine, and I'm back where I was. . . .Ah, those people at Bosch are going to know me well!
Have you cleaned the gas pipes and valve?
Are you refering to the valve on the water heater? Everything coming into the machine is clean, and I disconnected the regulator right before the water heater to see if it appeared to be functioning properly.I have not taken the gas valve apart. But now that I've disassembled everything else on the machine, why not?? !! It'll be fun!
I might be misleading you ,But I have found in the past "what changed" when this/a problem came up.
With rebuilding the water valve I think you might have knocked loose the block in the gas for a short time. But now its back. (fingers crossed this is it)
I have the same unit. 7 years now and the only problem so far is the pilot light went out one time due to VERY high winds.
I said early in this thread that I liked your idea about crud in the line. I have a friend who, after having work done on her gas line, started having weird problems (intermittent lack of flame) with her stove. I happened to be in her kitchen a couple of days after the problem started. She had a burner on, and the thing started to sputter, then there was a big ball of flame. She never had any more problems.
I guessed some pipe dope got in the line, then was slowly pushed along by the 3 psi or whatever, and intermittently/partially blocked the burner til the weak flame around it cooked it enough to blow through with a neat fireball. I have no idea if that's even posssible, but it was the only explanation i could come up with.
k
Any news?
Well, it's a long story. But I have a geothermal furnace and now I'm hooking up H2O to it. That was always my plan.As for the Bosch, I'm sure the problem is in the water valve. After I rebuilt it, I had hot water for 24 hours. I did some playing with it and decided to replace the venturi. (I don't know why Bosch doesn't include this in the rebuild kit.) At any rate, I get interesting fluctuations in pressure and heat fiddling with that. I have a feeling the O-rings on it are shot.Waiting for the new venturi now . . . and by the time it arrives, I'll be showering in water heated in the earth.Thanks for checking back. I don't get to this board too often. I don't understand how some folks do this and work, too.
Waiting for the new venturi now . . . and by the time it arrives, I'll be showering in water heated in the earth
Can you explain that hook up?
I'm familiar with a standard water heater and GSHP hook up. How are you doing it with a tankless WH or as a stand alone set up?
Right now the heat pump is heating the water in a heat exchange tank. It's one these:http://www.ergomax.com/E-Info.htmI'll be installing a back-up unit (haven't decided whether it'll be the Bosch or not) in the fall so that when I'm running radiant, I'll be sure there's plenty of water available for a shower.