Tankless: Fluctuating temp

[craigt-from-atl]

Model: Bosch 250SX NG
Installed: 10/2005

We have been experiencing fluctuation in temperatures pretty much since we installed the unit. The manual and CEC say that a pressure balance valve will help to solve this problem.

Where in the line do I need to install this valve? Does it need to be on the cold line before it splits off to the individual taps; or just before it enters the water heater? Or just before it enters the shower? (the shower is where we really notice it)

Thanks!
Craig

PS- Hank, no need for your input.

[rav12]

If the water temp fluctuates when other faucets are turned on then a pressure balancing valve may help. If not the problem may be something else.

I don't think I have heard of a whole house pressure balancing system although they may well exist. You can get pressure balancing valves for installation on individual showers. Many showers come with pressure balancing spools built into the cartridge.

Othe possibilities I can think of are that the gas line is restricted (too small), gas pressure too low or both. Also the flow impeller may be sticking inside the heater although it should not being a new unit but you can look at that as a possibility. On the 240FX you are supposed to clean this once a year as part of routine maintenence.

[tonyl]

Hey Craig,
Interesting. I was told to install the same thing for my Takagi TK-2 due to shutting off during showers. Went on for a year and a half. Cold showers for a minute and a half, then hot again. Installed a check valve just before the tankless water heater. Didn't help. In fact, made it worse.

Finally, a technician wanted me to remove the restrictor from the shower head to test. Upon inspection, there wasn't anything to remove. Was a cheap-o shower head from Target or Walmart for $3 at most.

So I went to Lowe's and bought a Moen with restrictor visible that could be removed if desired for a testInstalled it and WORKED LIKE A CHAMP!. Turned out the el-cheap-0 was BARELY enough to keep the tankless working. If someone jacked the hot water, the heater shut off. Showerhead was flowing maybe .7 gpm and as you know, you need .6 to keep tankless heater going.

FWIW....it might be worth installing a different shower head as water saver shower head was the root of my problem. Water saver shower heads seem to be incompatible with a tankless water heater. I changed the head in the other bathroom and we've had nothing but success.

Hope this helps, Tony

[craigt-from-atl]

Thanks for the replies, guys.

Hmm, replacing shower head sounds like an easy path to attempt to correct the problem. How can I tell how many GPM the showerhead is flowing?

-Craig

[craigt-from-atl]

If the water temp fluctuates when other faucets are turned on then a pressure balancing valve may help. If not the problem may be something else.


Well, it happens all the time, regardless of other faucets. Dead end there, I guess. :(


Othe possibilities I can think of are that the gas line is restricted (too small), gas pressure too low or both. Also the flow impeller may be sticking inside the heater although it should not being a new unit but you can look at that as a possibility. On the 240FX you are supposed to clean this once a year as part of routine maintenence.

We increased the gas line size to the specs recommended by Bosch. I do not know what pressure it's flowing at though. . .

I'm going to look into how many GPM I am currently flowing, but checking the impeller is a good idea as well.

Thanks!
-Craig

[rav12]

Yes does not sounds like other faucets are the problem here. With regard to the flow - you can either hook up a water flow/pressure gauge or use the"bucket method" - with this you just time water collected in a bucket and use this to calculate the GPM. However, this will not tell you if the GPM is fluctuating which is what is more likely to cause the fluctuating temp. The flow guages tend to use garden hose trpe adaptors so you may need to use some plumbing fittings to convert to measure the flow rate of the shower.

With regard to the other things - you can hook up a manometer to the gas pressure tap port on the gas valve on the tankles and again see if the pressure drops below min or fluctuates. This may help identify whether the problem is gas related. Typically you need a min of 5" WC at the gas valve inlet and 3.5" WC at the manifold. If the pressure at the gas meter is marginal then you could have problems even if the gas pipe size is correct. Also you could check the imprellor as suggested.

Finally I would suggest calling controlled energy corp. I've personally found the service techs to be pretty helpful and can help you troubleshoot this problem. They can also send you the ncessary service bulletins - they do not have everything for download - you need to ask them to send it to you.

Hope this helps.