Thankless tankless

We installed a new Bosch tankless water heater in 2008. The water temperature did not stay consistent when taking a shower. It was constantly shutting off and you would get a cold shower. We had the plumber that installed it check it and brought in a different plumber to check it and it still would not work properly. Out of frustration we replaced it with a new tankless water heater (different brand recommended by plumber) and had all new venting installed as well. It worked perfectly for about 2 months and then the exact same problem. We have intermittent hot water. Gas piping was checked for proper size and water supply was checked, filters were checked, flow was checked and we still cannot get the water heater to run steady while taking a shower. Is there a fix for this?

Brian O

How hot are you asking the tankless to be? It may be that if you have the set temp way high that when mixed with the cold at the shower, the hot volume isn't enough to keep the thing firing (it does have a minimum flow rate). Can you try lowering it to say maybe 45-48 degrees C which would mean you'd be using almost all hot in a shower and see if it makes a difference? Really low-flow showerheads may be to low to trigger the thing.

The alternative is to chuck the thing and go with a traditional tank or use it to fill an indirect and add a recirculation pump to keep the tank hot. That would add considerably to the cost. My very limited experience with tankless has led me to discount them as an option for my lifestyle. They have their good and bad points. You should be able to make yours work better than it is, though.

Without any of the particulars it's impossible to diagnose. The information we have so far is akin to, "We bought a Ford last year and it ran like crap so we replaced it with a different car that worked fine for a coupla months and now it doesn't. Can it be fixed?"

Tankless names/model...

...the capacity of your main gas regulator at the meter...

...number and size of other gas burners in the house...

...the plumbing diameters/distances & number of turns/fittings...

... the configuration of the gas runs to the gas burning appliances...

... is the problem isolated to showering or does it show up at all hot water taps...

...would be a good start.

Also is this coming off a city water supply or do you have a well pump? Fluctuating pressure, like coming from a pump with a 40/60 pressure switch can make the heater go on and off.

My first suspicion is an interaction/oscillation with the shower's mixer valve (which may be failing), but without more information, we're never going to debug this.

Just got this letter. Thought it might be appropriate here.


Dear Cary, I am an American expat living in Merida, Mexico. Recently I installed two CSV1, 50PSI Cycle Stop Valves in my home. One operates the flow of water in my house and the other operates the flow of water for my garden and fills the pool.

The house valve works great after much frustration with hot water surge experienced with a Bosch on-demand water heater. Down here in Merida we use city water but the water pressure is extremely weak. So I built a cistern, added a 1/2 hp submersible pump, pressure system, water softener and UV lamp. The pressure in the system was set to swing between 30 and 50 psi. The problem with this was that the Bosch unit heats water on demand and turns on and off by sensing flow. All of the water faucets and showerheads have different flow rates, with my kitchen faucet, a water saver, having the slowest rate of about 1.3 gallons per minute. Needless to say the problem I was having is that the flow rate was so slow at 30 psi in the kitchen, the Bosch unit kept going off at the bottom of the cycle.

Also, significantly in the shower, the 30 to 50 psi swing would vary the hot water temperature coming from the Bosch water heater about 4 degrees F. This caused great frustration when taking a shower since the water would pulse from warm to hot over several minutes. The pressure tank was 44 gallons and so it held about 12 gallons of water and took about 3-4 minutes to go through a cycle.

After installing the cycle stop the pressure stabilizes at 53 psi after going through a first cycle. The pressure switch is adjusted to 30 to 55 psi. All was well in the shower once cycle stop kicks in, but before then the first cycle still provides warm to hot water and then stabilizes. I read on your website that reducing the tank size was fine with cycle stop and so yesterday installed a 6 gallon pressure tank. Also, we set the switch to 35-55 psi. Now the first cycle has been reduced from 3-4 minutes to 15 seconds, about the time it takes the hot water to reach the shower head and so finally I have eliminated the drawback associated with a Bosch on-demand water heater and essentially have a water pressure system that operates 99% of the time at 53 psi or close to what I had back in America. Your product is just short of a miracle and has saved me the trouble of having to go back to a gas fired 50 gallon water heater which would have cost be about 3-4 times more to operate than the on demand system.

Before I close and I apologize for this long note, but I think it important that you receive this valuable market intelligence on your product and hope you continue to read.

Finally, I wanted to point out that I have recommended your product to several others down here in the Yucatan who are experiencing the same problem with the Bosch on-demand water heater. I have written to Bosch for advice and gotten no response. Fortunately, I read about cycle stop on-line and through my pool company, though your product is unknown by most of the hydraulics companies in Merida.

You might consider contacting Bosch Water Heating Systems to see if you can either do a deal with them or possibly tie your product to their water heater. In my opinion, after a year of frustration and much market research, I have concluded that an on-demand water heater which saves about 70% on LP gas provides unacceptable water heating without having your cycle stop valve to regulate water pressure. In fact, I would go on to say that if I were Bosch, I would not sell another on-demand water heater without either including your product or at least mentioning your product in the installation instructions.

I hope this long letter is helpful to your business. Also, for your info, I am building another house in Merida and will be using two more of your cycle stop valves in the process. I AM A BELIEVER! Best,
Steve

How about this scenario for you. Imagine your gas meter is undersized. Imagine it is rated for 175Kbtu/h. So, you're taking a shower and everything is great. You have it at a fairly warm temperature, but nothing too crazy. Say, you're water heater is only firing at half capacity and drawing only about 100Kbtu/h. Then, suddenly, your boiler kicks on. You have a pretty big boiler, and not the smart type that can modulate the gas down if it needs to. So, it kicks on full force and draws 150Kbtu/h. Now, your meter can only supply 175K, so something has to give. Your big dumb boiler doesn't feel the pressure drop so it keeps on firing. Your modern tankless water heater, however, knows that the pressure is too low for the amount of hot water it's trying to make and shuts down.

If this is in fact what's going on, it will throw an error code on the display. But if no one is around to read it, it will just go away in a few minutes. If you'd like to test if this is true, first check your gas meter to see what the rating on it is. You can add up the ratings on all of your gas appliances and see if they all fire at the same time whether or not your meter can handle that. The other thing you can do is set your digital camera in front of the water heater and hit RECORD. Go take a shower. When your shower goes cold, something has happened. Go back and check your camera to see the code. If there is someone in the house that can help you, just have them turn up the heat while you're in the shower. The boiler/furnace will kick on. If the water heater trips up, have them run down and look at the display. Check the error code against the instruction manual and see what's going on.

To me, two different branded tankless water heaters doing the same thing in the same home, that screams "gas issue". If you find this to be true, you can call your gas supplier and ask for a larger spec meter. They may be pains in the butts about giving you a new one, but you can try.

Good luck!

Mr. Tankless
Expert on WechSupport.com