Water Heaters - Insufficient water column pressure at inlet

My Bosch Aquastar Model 125 HX LP was installed by heating and cooling installer unfamiliar with the unit.

We are off the grid at a cabin - and it works fine in the summer months, but delivers mildy warm water in the winter months. It does not deliver shower ready water in those months.

We have two 80 # propane tanks delivering propane. All other appliances work fine in the cabin, but I understand the BTU and 'water column pressure at the inlet' demands of this unit are higher.

I tested the inlet pressure as per the unit installation and operating instructions and found 8 " water column without demand and a drop to under 4 " with peak demand. The unit calls for a minimum of 11 " without demand and 9" at maximum.

The piping is black pipe and complies with the requirements of installation - so I assume we are looking at tank size or the regulator, correct?

The tanks consist of 2 - 80# tanks with a regulator set up to operate from either tank.

Thanks for whatever you have to offer here.

One of two things could be going on as long as the gas line to the water heater is correct.

First is the regulator @ the tanks need adjustment or replacement. A pressure reading would need to be taken @ the regulator and see what the lock up (pressure with the heater off) and flow (pressure with the heater running) are. If the pressure is not sufficient at the regulator it would need replacing.

Second possible problem is the propane in the tanks not vaporizing enough pressure to the regulator. This happens when the tank is running low in cold climates. This is likely the culprit to your problems.

While I don't have the vaporization rate for a 80# tank, I'll give you the rate for a 100# tank. A 100 pound tank will only give you 52,400 BTUs @ 30 degrees when the tank is 25 percent full. Being your water heater requires upwards of 120,000 BTU's to work properly, this is an issue.

Solutions are to either piggy back multiple 80# tanks together (at least 3 or 4) or get a 420# tank (holds 100 gallons). The problem is with the later you would need a propane delivery company to fill it on site.

My regulator does not have a fitting that allows the monometer to connect for a test.

Could I insert a fitting in the line coming out of the regulator? And do you have a source for such fittings?

Second set of questions on the regulator - are there ways to tell what pressure and flow levels a regulator is set up to handle? There are no obvious specs on the outside of the regulator.

Thanks for this information. You are really helping me figure out a long term problem.

Could I insert a fitting in the line coming out of the regulator? And do you have a source for such fittings?



You should be able to get a fitting to adapt to the threads of the regulator outlet from a plumbing supply store. Even if you get a tee with the appropriate threads for after the regulator and connect a hose barb to the tee end for the manometer.

Second set of questions on the regulator - are there ways to tell what pressure and flow levels a regulator is set up to handle? There are no obvious specs on the outside of the regulator.

You need a standard twin stage propane regulator capable of providing a minimum of 125,000 btu. A ordinary bbq regulator won't quite cut it. Even if you get low pressure at the regulator, it could be due to low pressure going into the regulator from the tanks.

Thanks - you've given me solid info to work with.