Fluxuating Shower Temperature / causes tankless water heater to error out at times

Plumbing Forums

Help Support Plumbing Forums:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

tigg2

New Member
Joined
Jul 12, 2015
Messages
4
Reaction score
0
Location
,
The shower water temperature fluctuates (tub/shower combo)- this seems to only occur in the shower, and I am not making other demands to the water supply (such as flushing toilet/running dishwasher, etc). The temp remains constant when drawing water for the tub, running the faucets in the bath sink as well as the kitchen. I can't say I notice a big, if any, change in water pressure.

This is what happens. I turn on the shower, and get the water adjusted to where it is comfortable. After about a minute it may get cooler or warmer so I try to adjust, trying to chase a comfortable temp. Sometimes it works, sometimes the hot water heater will actually error out and then all I get is well water cold water. (brrrrr)

I am on a well.

The manufacturer for the temperature control is Moen and I recently replaced the cartridge insert, thinking it might be the cause. It is not.

The bathroom and kitchen sink have what appear to be water temp regulators plumbed in. These are red capped pvc "knobs" (looks like the end of business end of a torpedo) that spin. I do not know if there is one buried in the wall of the shower and if there is, if it would cause the problem I'm experiencing. I'm thinking it would be installed after the tub faucet as that appears to be working fine.

The water heater is a Navien tankless, and will sometimes throw an error out (failure to ignite) during the shower once the temp starts to fluctuate.

I hope I've provided enough info for someone with alot more knowledge than I to make a educated guess as to what I should to to either fix or continue to troubleshoot the problem.

Thank you,

Carolyn
 
Not sure if provides any additional information but I was reading elsewhere that there could be a cross over issue between the hot and cold. I unplugged the water heater (propane) and turned off the cold water access to it.

All my faucets are single handle controls. The kitchen sink faucet and bathroom sink faucets (I have a second bathroom with sink and shower/tub combo I don't use) would give good cold water flow on the cold water side and a small trickle and then no water on the hot water side. I understand that means there is no "crossover" of hot and cold at these points.

The tubs were a different story. I was only able to get a small trickle out of either faucet when I asked for cold water and the trickle was the same when I went "full" hot. then I did some research (after taking the control handle apart again and not finding a problem), found out these have posi-temp cartridges and I won't get flow if the pressures aren't equalized so I put it back together again. Plugged in the hot water heater and turned on the water to it. I asked for cold water out of the upstairs tub/shower faucet and got cold water, it did not trigger the hot water tank to come on. I asked for hot water from the same faucet and I got hot water.

The downstairs shower is different. I don't get straight cold. When I ask for water it triggers the hot water tank to come on.




Does that help?

Carolyn
 
Last edited:
The Navien is a CR-180 that was installed in '08. I've never been happy with it as it seems to struggle igniting at times but once lit, it stays lit. I'm told it may be because the yahoo that installed it only ran a 1/2" line from the 3/4" main gas line. I tend to get 03 ((ignition failure) or 48 (abnormal gas pressure) error codes. My propane tank is 500 gal buried and was just filled. I'm going to have to have a new, properly sized line ran but it ticks me off to have to pay for some else's poor work. it isn't as if it doesn't say right in the installation instructions the proper sized line to use.

I spoke to my nephew about what I thought were temperature regulators and he laughed and said, no, there were just weird looking shut off valves. Sorry for the confusion.

I don't know why I never noticed I wasn't getting but a little cold water out of the downstairs shower faucet.
 
Last edited:
Pulled the cartridge and reinstalled. I'm assuming, though it was new, something was "stuck". I have good cold water out of the faucet now.
 
Back
Top