Combi acting funny after descaling

[CallmeJake]

Hi,
I have a Noritz combi boiler that was installed ~5 years ago along with a dedicated on-demand recirculation line. This setup has been working fine and we've been happy with it.

I remembered to clean the air and debris filters and descale yearly until I forgot and got a reminder earlier this year. The unit set a code and wouldn't make hot water. I looked it up and the cause was mineral build up and the fix was to run the descaling procedure, so I did that and cleaned the filters. Now it runs well again and hasn't set another code.

The reason for the post though, is that it has sporadically started taking a really long time (7+ minutes) to make hot water in some cases. The first time it fires after sitting for a while it will make hot water no problem. But then sometimes if you try to use it again shortly after it won't, the unit will act like it's firing, the pump will come on and the flame icon will show, but the water coming out of the unit is just straight cold water. It will sit like that for minutes with the water running or the recirculation pump on and then the fan will ramp up and then it sounds like the unit actually fires and hot water will start flowing.

For a fairly repeatable scenario, my wife usually showers in the morning around the same time. I'd have the recirculation pump programmed to run around that time so the water was warm and it worked well for the past 5 years. After the cleaning, the water at the tap would initially be hot from the recirculation but then almost immediately get cold and after letting it run forever would get hot again. The first couple of times it took so long she thought it was broke and gave up on the shower. (Those were not great mornings haha). So I stopped having the pump run, now she lets the water run for <1 min and gets hot water. Once it gets hot, as long as you don't turn the water off it will stay hot. So if she got in while the initial recirculation was running there was no problem.

It seems obvious that I messed something up when I cleaned it but I don't understand what that could be. I followed the procedure in the manual the same way I've done in years past and had no problems. The unit itself isn't setting codes.

Appreciate any thoughts or help.
Jake

 

[Breplum]

I stopped taking Noritz trainings years ago, but sounds like flow sensor may not be registering consistently. With Navien, I can pull up flow right on display. See if you can pull flow up to check, if you have that capability

 

[Sponsor]

 

[CallmeJake]

Sorry for the slow response. I found the flow read-out but was having trouble getting the cold water issue to happen while I was standing there, maybe that's the fix just watch it?

Anyway, when it is working normally or when it's only flowing cold the display shows around the same flow readings, between 2-3 GPM.

Today I had a hose on the service valve at the outlet of the unit and was using that to run the hot water. After 3-ish 5 gallon buckets the water got hot again. When it first came out it was really hot, like steaming, once it flowed for a second it came back down to 'normal' hot. Seemed like the water was just stuck in there?

I don't how these unit work, is there a valve or something that could have gotten something stuck in it during the cleaning?

Thanks again for the help

 

[Breplum]

not familiar with noritz anymore, but mixing valve would be almost the only other part if indeed the burner is "on" and you aren't getting pure hot.

 

[CallmeJake]

Appreciate the feedback. The display claims the burner is on and while I was standing there I could hear the ignition but I didn't take the cover off and look through the glass.

If that were to be the issue, are they typically serviceable or replaced?