Tankless startup noise

Dread27

Kieth
The reason for the grone noise is usually on low fire of the unit because the CO2 level is lower than what the factory recommendation is, which is NG 8.4% or LP 9.8 %. The only way to fix this is to put a combustion analyzer test on the boiler and adjust the gas valve.

Keith_31

Tankless startup noise

Hi,

Anyone have any experience diagnosing a startup noise on a tankless gas eater?

This is Baxi Luna 380 installed in Jan '08. It runs both hot water and baseboard heat.

When the unit turns on in the early morning (and occasionally late at night), it emits a groan that starts soft, gets very loud for about 4 seconds, then soft again. It can be heard in the other room even.

The installer was out this morning and couldn't re-create it. They said everything is in spec though.

Any idea where to start diagnosing this? The only alternative seems to be to try to get somebody out at 3am.

Thanks!

Keith_31

Keith_31

Tankless startup noise

Thanks for the quick response!

Any idea why it would only occur at night, not all the time?

Thanks

Dread27

Because the high and low fire rate are set up on the heating side of the boiler, so saying that during the night is when the heating cycles work the most and the boiler acctually go to low fire more often because it is trying just to maintaning temperature from the reading of the CH HTC sensor. The boiler goes into low fire all of the time in the heating mode but does not see low fire in the domestic hot water mode.

Nron_13

I have a Ever hot /Rinnai in my shop that makes the same type of noise and I find that it cant maintain the high fire calibration if ajusted and then left oner night it howls on start up for a couple of min then you can see the system correct it self as it comes up to temptrature
dont know whats causing it yet

Nron_13

any Idea's

Blackoakbob

Moaning boiler...

I have a Knight that does it when running at low fire start up. It's sized for snow melt but runs an indirect and backs up a geo thermal buffer tank, so it runs at low fire alot. I will run another combustion test when I go back to fix a small leak that showed up a couple months after start up. I did adjust one other Knight and it worked just fine.Best Regards,
Oh, regrets to all that attended Wetstock Denver, I was one of those that had their flights cancelled last week, so I returned home to 16 inches of snow!

Kal Row

dont forget gas pressure...

it varies - it's especially low early morning when everyone’s system turns on - anyway, it will make condensing boilers sing, especially those with the venturi gas valves - of which the knight is one example, because the gas pressure closes the flow and the venturi suction opens it – and the flame front vibrates, it acts like the reed throat of a 16ft pipe of an old style church organ.
I had a knight 500 running on a 250kbtu gas meter and it sounded like a steam locomotive until I got the rotary meter in and now it’s dammed near silent

Yeah!! That’s the ticket!! “a concerto for condensing boilers!!!!” I’ll give professor Peter Shickele aka PDQ Bach, a call…

Be happy it even runs – many of the delayed acting gas valves used on natural draft steam boilers never open stage two, and the unit doesn’t produce steam even though it looks like the fire is on full – it’s just producing 1/3 the btus and cant get through the pickup cycle, another problem with those is fine powdery debris on the inlet screen and has the same effect – you can tell it’s that, because you dont have the wind woosh roar sound from the flame on full

So check your inlet and outlet gas pressures with a digital Manometer – the water tube Unometers are two slow