Minimum flow needed to light has increased, Noritz NRC1111-DVNG

[Lifespeed]

I installed a Noritz NRC1111-DVNG in 2012 along with a larger gas regulator, 1-1/8" gas trunk line feeding a 1" branch line, and 1" copper water supply along with a Readytemp external recirculator pump and controller. A backwashing carbon filter followed by water softener (both Fleck 7000SXT) were installed at the same time and have been in continuous operation with the softened water tested periodically to confirm proper operation. The heat exchanger was descaled with vinegar three years ago. I have not been descaling annually as this should not be needed with the treated water.

Recently I noticed the water heater would not light from bathroom faucet flow unless it was fully open. If the cold water handle was opened as well, reducing the hot water flow slightly, the water heater would shut off. This is definitely not the same minimum flow rate it had over it's six year life. I haven't measured the flow of this faucet yet, but I would guess it is more than 2GPM and has certainly been more than adequate to light the water heater in the past, even when partially open.

Any ideas as to what might be going on here? I do have the remote control panel installed in this bathroom, but do not see any error codes presuming they would be indicated on this panel.

 

[Dana]

Flow detectors often fail over time, so it's likely that yours' time is up. (They can fail really quickly in heavy-use, high flow conditions, such as when the tankless water heater gets used as a hydronic space heating boiler.)

 

[Sponsor]

 

[Lifespeed]

Flow detectors often fail over time, so it's likely that yours' time is up. (They can fail really quickly in heavy-use, high flow conditions, such as when the tankless water heater gets used as a hydronic space heating boiler.)

I was wondering if that might be the case. Hopefully they designed it to be easily serviceable.

Edit: spoke with Noritz. I will try the universally-recommend flush (unlikely) and then call their tech support with a voltmeter while I am standing in front of the unit with an assistant operating a faucet. Will also measure what the minimum flow rate is now. I still think the flow sensor is a likely culprit, but may as well go through the proper procedures first. At least it hasn't conked out completely, can still take a shower and the recirc pump flow is high enough to light it.

 

[Jadnashua]

If the vanity faucet is not ancient, it's flow restricted to a max of 2gpm. Many tankless systems minimum flow turn on is in the order of 1/2gpm, so unless you're dribbling the water out of the faucet or it is barely set to warm, you'd probably exceed that. Some will need a bit more, but once turned on, will stay on when the flow is lowered. Don't know the specs on that unit.

 

[Lifespeed]

If the vanity faucet is not ancient, it's flow restricted to a max of 2gpm. Many tankless systems minimum flow turn on is in the order of 1/2gpm, so unless you're dribbling the water out of the faucet or it is barely set to warm, you'd probably exceed that. Some will need a bit more, but once turned on, will stay on when the flow is lowered. Don't know the specs on that unit.

Agreed, something has changed. It used to light at reasonably low flow rates. It should be a 2 GPM faucet, but I'll check.

 

[Jadnashua]

Softened water may slow the requirement to demineralize the unit, but it may not make it unnecessary. I'm not sure how they detect flow. It could be that there's a little paddle wheel or vane in the water stream, and a little mineral deposit on it could make it sluggish to respond...a good cleaning may make it work again. I'd try that first.

 

[Lifespeed]

That is the plan. On vacation this week, will post results or lack thereof next week.

 

[Lifespeed]

I flushed the water heater with vinegar for three hours, it works fine now. Nice not to have to diagnose and perform yet another repair on the house. I guess I can't go three years without flushing even with soft water. Interestingly, the brass hose end returning the solution to the bucket plated with copper from the copper that went into solution thanks to the weak acid.