Flow sensor adjustment for Navien 240S natural gas fired tankless water heater

Question

We installed a Navien 240S natural gas in our house, and it is working fine.

Except the short range for hot water valves in the showers. So, in other words, I need to turn shower valve almost all the way on to start the hot water. This leaves us a very small range to adjust hot water when taking a shower. My plumber explained that it is because the sensor is triggered only with a certain water flow. In general, the water pressure is high already. But there is just not enough flow until I turn the faucet almost all the way on.

Is there way to adjust the flow sensitivity for the sensor in the water heater?

My plumber suggests the following:
He can install some flow controls on the cold water pipe in each shower and set them to desired temperature range.

Is this a good solution?

I find it strange that I cannot adjust that sensor on the unit.

ArchonOSX · Answer

This is a common complaint for these types of water heaters.

Unfortunately, you have a model that seems to be slow to respond to water flow. I don't think any company has a way to adjust the flow sensor on their on-demand water heaters. This is not a customer adjustable function of these style of heaters.

If you're dissatisfied with this product I would suggest searching for a company/product that has positive reviews from people for the product's low-flow response rate. Some products respond even respond well to just running a hot water valve at a trickle.

Good luck!

DDS · Answer

Best solution is to rise the difference between primary water and DHW. Usually is not only the water flow to trigger the boiler, but a low temp on primary water. On most boilers primary water is kept 20°C above DHW.

My 15 years old Hermann can handle as low as 2,5L/min, so I think you have a setting problem on the boiler' computer.

EDIT:
According to your boiler specs, the minimum flow rate for your boiler is 1,9 L/min.

I suggest you to lower the DHW temperature on the boiler, 55°C usually is enough, on your biler, so more hot water is required to flow trough the termostatic valve in the shower (and trough the boiler) so the boiler flow won't fall under the minimum.

David · Answer

I find the very BEST fix on almost any tank-less hands down is to install dual handle faucets then you can turn the hot water on higher keeping the flow high and adjust the cold water to the perfect temp this also gives you a lot more water pressure and NO more hot water drop off.
if you don't have that option then you have to turn the temp down on your heater so the water flow is not to slow for the flame. its all about flow if the flow is to slow then the flame could over heat the boiler coil and that can cause the coil to steam and explode so it shuts off to prevent damage to the coil. So lower flow = lower flame.
I tried temperature flow control sensors and my tank-less has issues with them and still was getting the hot water drop off and low water pressure. hope this helps.

m sheridan · Answer

Clean the shower head strainers or remove the flow restricted from the heads

Flow sensor adjustment for Navien 240S natural gas fired tankless water heater

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