Noritz...scalding or cold

[JackieO]

We've had a Noritz tankless water heater since 2006. It is installed in the crawl space under our master bath. Our shower has a single handle which turns left and right for temp control. I can't figure out why we cannot get "warm" water in the shower. It's only HOT or COLD no matter where I have the temperature control handle sitting. When we start the shower, it's very hot. When I move the handle ever so slightly to where it would normally be a warm setting, the water turns cold and I have to turn it back to hot before the water warms up again....and then it's HOT again to the point of scalding.

Where would the problem exist? Is the the faucet? Is it Noritz? Somewhere else? It would be great to be able to take a warm shower again.

 

[Wrenched]

We've had a Noritz tankless water heater since 2006. It is installed in the crawl space under our master bath. Our shower has a single handle which turns left and right for temp control. I can't figure out why we cannot get "warm" water in the shower. It's only HOT or COLD...

Where would the problem exist? Is the the faucet? Is it Noritz? Somewhere else? It would be great to be able to take a warm shower again.

It sounds like a valve/cartridge issue. Tankless units usually just put out hot water under flow conditions and for the most part do not modulate the temperature. Unless the issue started exactly when the tankless was installed, I would focus on the the shower valve first.

Can you upload a picture? What make is it? How old is it? Did it work properly at one time?

 

[Sponsor]

 

[Jadnashua]

The flow sensor in the tankless system may be sticky...each of them has a flow sensor that tells it when there is a demand, and that triggers it to turn on. At full volume (hot), it appears that there's enough, but as you back off, you're using less hot water, and the tankless now thinks there isn't any flow, and it doesn't need to run. This can be more of a problem in the summer when your cold water is nearly room temperature...it then takes very little hot to be comfortable in a shower. In the winter, you need lots more hot to get the same mixed outlet temperature. I'd look at the flow sensor.

 

[JackieO]

It sounds like a valve/cartridge issue. Tankless units usually just put out hot water under flow conditions and for the most part do not modulate the temperature. Unless the issue started exactly when the tankless was installed, I would focus on the the shower valve first.

Can you upload a picture? What make is it? How old is it? Did it work properly at one time?

 

[JackieO]

It was installed when we built the house in 2006. As I recall we didn't have this problem in the beginning. My husband had someone come look at it a few years ago and the plumber said He couldnt find a problem.

 

[Jadnashua]

So, the thing is about 11-years old...how often have you delimed it? Normally, that's an annual service that should be performed. One of the hassles of a tankless system is that they do require regular maintenance and, not all plumbers are schooled in how to maintain or fix them.

 

[Wrenched]

Jadnashua is right that flow condition issues could cause a problem like this. The tankless shouldn't fire below 0.5 gpm; the flow sensor tells the boiler when to fire based on flow in the hot water supply piping.

A damaged/sticky flow sensor, an incorrectly installed flow sensor, or some combination of flow restriction (e.g. ultra high efficiency showerhead, a mineralized showerhead, very low water pressure, etc) and high set point on the tankless could cause this problem.

This can be tested for. First off, all fixtures supplied by the tankless should be affected. Second, if this is the case, the problem should disappear if hot water is run from another fixture while the shower is in use.

If another fixture, a hand sink for instance, has uninterrupted hot water water(ie, the tankless is firing) while the shower still experiences a temperature cliff, the issue is likely at the valve itself.

Can we get a picture of the shower valve and head? Are you on city water or well water? Do you know your water pressure? What all does the tankless serve? Do you know what temperature it is set at?

There are a handful of more complicated/unlikely possibilities that might cause a problem like this. Usually it's best to test for the easiest things first.

 

[Valveman]

Do you have city water or a well pump. Cycling on and off from 40 to 60 with a well pump causes that problem as well. You might consider turning the temp down to what you want in the shower and run hot only.