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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8768
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Baxi Luna 310 Fi, installed by me in April 2007 in

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I have a Baxi Luna 310 Fi, installed by me in April 2007 in my cabin in the Rocky Mountains in USA. Has been working great, but last fall it started whining/screaching when ever there was demand for hot water. Since I installed it I also do the routine servicing recommended in the manual (Sec 7.x). I recently cleaned/flushed the main heat exchanger.

Looking for the next step to resolve DHW screaching. I think I need to flush/clean the Plate Heat Exchanger next. Agree? Do I need new What do you recommend for cleaning the gunk out? CLR? How to you recommend flushing it? Should I also disassemble clean the Diverter Valve and Manifold as it has water running through it? I don't see a need to touch the DHW Pressure Differential Valve as not water actually runs through it.

Finally, I do not have any inhibitor propylene glycol solution (25%) in my closed system. I was going to add it after I resolve the DHW screaching. Any suggestions on a product to use and where to get it?

Thanks for any help/suggestions you can provide.

Welcome to Just Answer!

You and your neighbor already have demonstrated more knowledge of this issue than the vast majority of people in the paving and road construction business...

The reason you have not gotten an answer so far is that soil studies will be required to go beyond what you already know.. and any advice without soil and drainage studies will be nothing but wild guesses, and not in your best interests.

You can most likely do what you have in mind and be better off than 99% of projects in the area however. Beyond that you need to contact a civil engineer, who will order soils analysis (not cost effective on a project of this type in most cases)... then he will give you his advice, and that advice will likely not be much better informed than your own unless there are unusual soil conditions that I do not expect.

Stay in touch if you need to. Since this is not an answer to your question I am posting it as an info request only.


Customer: replied 4 years ago.

I do not see how the info has anything to do with my Baxi Luna question. Is this really the info you intended to send to me?

oops! My response from another question (about driveway construction) got pasted to your question... that was either my mistake or a server error.

Please disregard it.


Regarding your Baxi Luna however, it is not common that a dirty heat exchanger results in any noise... it is more common that the noise you describe is coming from the fan motor.

Regarding cleaning acid solutions, white vinegar pumped through the heat exchaner for a few hours at over 5 gpm will work as well or better than CLR and a tenth the price... it is also recommended by Baxi and many other water heater mfgrs.

You can buy a mechanics stethoscope at any auto supply store for under $15 in most cases and use that to pin point the noise.

Look that over if you wish and get back to me.

We can go from there.

Customer: replied 4 years ago.

Correct me if I am wrong, but I believe there is only one fan and it is above the primary heat exchanger at the top of the unit. It runs for both heating and DHW. I only have this sound when DHW is called for. Is there a second fan that only runs when DHW is demanded?


Thanks for the info on white vinegar and stethoscope.

Hello again, indeed there is only one fan, and it runs whenver the burner is on in either central heat or domestic hot water mode...there is no second fan.

Your observation does indeed point to the heat exchanger. A dirty heat exchanger however seldom screeches... it could but it is more likely a valve that is not operating properly.... Use a mechanics stethoscope to determine the source of the sound.

Let me know how that goes.

Customer: replied 4 years ago.

I had thought it was a valve somewhere, even one in a sink or bath, so I turned them on one at time but the screaching never quite. As for a valve in the Baxi, it almost must be the Diverter Valve as it is the only one that operates when the DHW is called for. How do I use a mechanics stethoscope? I assume I drain the system and run it up the pipe. what am I looking for? With the system off (no DHW demand) the value will be in the "quit" position.


Hello again, to use a mechanics stethoscope, fit both ear pieces, then press the metal probe to the part of the boiler you wish to listen to... it will become obvious which part is making the noise.

Take your time... that pays off, it takes a while to make sense of these sorts of things.. your testing approach so far is right on target... you just need to be using a stethoscope to pin point the source


You can also sometimes feel the noise vibration with your fingers.. give that try also.


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