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Old 03-09-2017, 07:45 PM   #1
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Propane pressure / on-demand water heater question

I'm trying to troubleshoot my on-demand water heater, Precision Temp said check water pressure & gas pressure. Water pressure is good, not too high or low I think and a full gas tank. So my question is, can 40yr old gas lines get gunked up in any way and secondly, is it possible to check gas pressure through the system? I've noticed that if water heater running the stove gas pressure is non-existent.

many thanks !!
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Old 03-09-2017, 07:56 PM   #2
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More likely the regulator at the tank(s) is worn out.

We have the Trump AquaGo comfort on demand water heater and we can run the replacement Dometic CU434 stove at the same time we are getting hot water along with furnace operation in both our 2015 23D International Serenity and 2014 Classic which have similar modifications.

Note that we removed the stock gas/ammonia refrigerators in both trailers and replaced them with Vitrifrigo refrigerators with 12Vdc Dan Foss freon compressors that draw about ½ amp (68 watts when running). We have a 300 amp hour lithium battery (with five 100 watt solar panels on the roof) in the 23D and a 600 amp hour lithium battery (with nine 100 watt solar panels on the roof) of the Classic. There is adequate power to run the refrigerators for days since one can safely use 90% of the power in a lithium iron phosphate battery.
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Old 03-09-2017, 10:05 PM   #3
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great to know, I need to check that, was thinking reg was newish .. worth swapping out and seeing if that makes a difference. thanks..

i'm looking for a new fridge too as it happens, don't think i'm up for solar installation yet but would love to read more about that ...
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Old 03-09-2017, 10:38 PM   #4
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question on those fridges, so they run just on electricity, with those batteries, how long would they last between charges ? thx
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Old 03-10-2017, 01:58 AM   #5
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You well need a manometer to check your gas pressure. Post regulator pressure is very minimal or low. If I remember correctly about 11 w.c. is ideal.
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Old 03-10-2017, 11:15 AM   #6
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Yes; pressure is about 11" WC for propane after the regulator.
You can make your own Manometer using a piece of clear plastic hose held in a U Shape filled with water You will need at least 36" but 4 ft would be better. When pressurized the difference in the two legs is your pressure measured in inches of water column. (WC). However if the regulator is somehow plugged, it may register good pressure with little or no flow. It should be able to maintain the 11"WC while all appliances are running.
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Old 03-10-2017, 11:30 AM   #7
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If your rubber hoses are very hard you need to race them also.
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Old 03-10-2017, 11:50 AM   #8
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BTUs. The on-demand takes a lot, fast. 100,000 to 200,000, maybe 4 times what the little 5-gal. heater took. The regulators on your tank connection are almost certainly too small for the heater by itself, never mind the combined loads of water heat, furnace, stove & refrig. Also, piping is going to be so small as to restrict gas flow.
Got a buddy in HVAC? Get him to size everything and tell you your options. Might be that he can put a 5 psi reg. on tank and drop to final ½ psi at each appliance.
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Old 03-24-2017, 11:19 PM   #9
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BTUs. The on-demand takes a lot, fast. 100,000 to 200,000, maybe 4 times what the little 5-gal. heater took. The regulators on your tank connection are almost certainly too small for the heater by itself, never mind the combined loads of water heat, furnace, stove & refrig. Also, piping is going to be so small as to restrict gas flow.
Got a buddy in HVAC? Get him to size everything and tell you your options. Might be that he can put a 5 psi reg. on tank and drop to final ½ psi at each appliance.


Great advice all, much appreciated
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Old 03-26-2017, 08:41 AM   #10
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We can run the stove (Dometic CU434 in both trailers), furnace (34,000 BTU in the Classic and 25,000 BTU in the 23D - same size as in 25/27 foot models) and the Truma AquaGo comfort (60,000 BTU and flow rate of around 1.5 gpm) water heater at the same time in both the 2014 31' Classic and the 2015 23D International Serenity. Having said that, the Classic has the stock aluminum 40 pound propane tanks and the 23D has the stock 30 pound propane tanks and both have the original propane gas lines and regulator.

In cooler weather, a 20 pound propane tank might not be able to vaporize enough propane fast enough for the three appliances to run at the same time.

At home, we have a Rinnai 7.5 gpm (gallon per minute) instant on water heater (180,000 BTU) that requires a ¾" ID gas line.
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Old 03-27-2017, 11:12 AM   #11
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We can run the stove (Dometic CU434 in both trailers), furnace (34,000 BTU in the Classic and 25,000 BTU in the 23D - same size as in 25/27 foot models) and the Truma AquaGo comfort (60,000 BTU and flow rate of around 1.5 gpm) water heater at the same time in both the 2014 31' Classic and the 2015 23D International Serenity. Having said that, the Classic has the stock aluminum 40 pound propane tanks and the 23D has the stock 30 pound propane tanks and both have the original propane gas lines and regulator.

In cooler weather, a 20 pound propane tank might not be able to vaporize enough propane fast enough for the three appliances to run at the same time.

At home, we have a Rinnai 7.5 gpm (gallon per minute) instant on water heater (180,000 BTU) that requires a ¾" ID gas line.
Great feedback, thanks ... I wonder if that's the issue, gas line is too narrow?, no has mentioned that yet so suspect not the issue, but maybe. I need to change the regulator and see if that fixes first, then look at adding a new larger diameter line ?
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Old 03-27-2017, 11:14 AM   #12
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Originally Posted by roebling View Post
BTUs. The on-demand takes a lot, fast. 100,000 to 200,000, maybe 4 times what the little 5-gal. heater took. The regulators on your tank connection are almost certainly too small for the heater by itself, never mind the combined loads of water heat, furnace, stove & refrig. Also, piping is going to be so small as to restrict gas flow.
Got a buddy in HVAC? Get him to size everything and tell you your options. Might be that he can put a 5 psi reg. on tank and drop to final ½ psi at each appliance.
good idea, thanks ... i need to ask around re HVAC ...
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Old 03-27-2017, 11:29 AM   #13
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New gas lines for On-Demand water heater ?

Hi .. wondering if anyone has had to change the gas line for an on-demand water heater ? seems like I'm not getting enough pressure, going to check the regulator but it's only about 3 yrs old and rarely used ....so can't imagine it's failed already.
My gas lines are from 1972 ! so maybe wider diameter on newer airstreams ?


thanks
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Old 03-27-2017, 11:58 AM   #14
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Quote:
Originally Posted by nickclifford View Post
... can 40yr old gas lines get gunked up in any way ...!!
Answer: Yes!

LP gas is derived from petroleum and over time some of the constituents may condense and coalesce into a dark, oily liquid. This can "puddle" in low points in the system and restrict gas-flow.

It's rare, and it usually takes a period of time to do so, but you might wish to blow out your lines. (Disconnect any appliances and regulators when doing this to avoid damaging them. Be aware any liquid in a low spot might only be spread throughout the system ...to later re-assemble and continue it's blockage....unless you disconnect the low spot and catch the liquid at the next available fixture or connection. A suitable solvent or detergent, followed by drying with air can be called for in extreme cases.)
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Old 04-05-2017, 10:44 PM   #15
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Took the regulator to local RV place for pressure gauge test....( regulator is only 3 yrs old and very low usage) anyway, the gauge showed the regulator to be functioning normally but my RV guy said not always accurate and that regulators have a habit of malfunctioning quite regularly, so he suggested trying a new one. Bingo!! That was all it was, hot water is now piping hot again.
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Old 05-25-2017, 07:18 AM   #16
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Marshall has a higher volume regulator/auto switchover valve available. It has green paint to identify it from the others. It may help for instant hot demand. I have no experience with them, just saw them at the RV Store.
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