flush combustion side of heat exchanger for Dunkirk/Utica 95M-200

cas1717

I have a Utica UB95m-200 .This model is also sold as Dunkirk Q95-200. Made by ECR International.

The heat exchanger is sealed cast aluminum and same as in the Q90 125-200 boiler.

The manual from ECR says "Aluminum oxide deposits may be
rinsed away by inserting a hose into the burner opening of
the casting and slowly running water through the flue side
of the boiler and out the condensate drain"

I plan to do the flush myself as I already know the consequences of not doing the cleanup.
My HX was replaced in 2022 under warranty because the exhaust developed a hole from corrosion due to acidic aluminum oxide that builds inside the combustion chamber.
Could not find a contractor in my area (South Connecticut) to flush the aluminum HX. I did hire for annual maintenance but they brushed the igniter and run combustion analysis and checked for leaks, blockages, etc.

Hoping to find on this site somebody who's done the combustion flush on the Q95 or the Q90 model .
I'd appreciate any hands-on practical advice beside what's in the manual.
- if they used any chemicals . Like the Axiom F9-AL.
- is it ok to connect a shop vacuum to the drain
- how to check that no water is left in the combustion chamber (w/out taking apart the rubber gasket connecting the HX to the exhaust assembly).
-anything else to look for

cas1717

I did the flush myself . In case somebody else wants to DYI this task , my feedback is as following.

Preparation:

Get a 3 feet long 4" diameter water hose with clams . Amazon has them in 25 feet . Or get a 3" diameter and use a heat gun to make it larger like I did. You need about 3.5" diameter.
Get a small wrench for the square cap at bottom of exhaust column. The space is very tight.
Get a shop vacuum.
Get the 3 grafoil gaskets : Grafoil Burner/Casting Gasket, Burner-to-Flue Adapter Gasket, Igniter Gasket .
You may not be able to re-use the old ones.
Get a shower head or a garden hose with a spray pattern

What I did step by step:
1) I read the steps from the 95m-200 manual. Obviously, I cut the gas and the power to the boiler :-)
I started the process when exchanger was slightly warm to the touch .

2) I removed the 2 screws between the gas valve and the blower motor.
The Manual recommended to undo the gas union but it was stuck and I did not want to deal with metal-on-metal unions . In hindsight, I disagree with the Utica manual that somebody can remove the gas valve + blower + burner as one unit , smoothly , perfectly horizontal without having the burner's mesh touch the sharp edges of the access hole in the exchanger.

3) I took out the igniter .

4) I took out the blower and the burner as one unit.
The tolerance is very small and the burner mesh did touch against the sharp edges of the access hole in the exchanger.
The burner mesh had a tear already and it got worse as it caught against sharp edges of the hole as it was hard to maneuver the heavy blower .
I wanted to change the burner anyway and I had a spare as the old one was 16 years old.
Next time I will do the wash, I will carefully separate the grafoil gasket and take out the blower first and then maneuver the much lighter burner out of the exchanger keeping it perfectly horizontal and without touching the sharp edges of the access hole.

5) I inspected the inside of the burner. Moderate aluminum oxide residue visible on the walls .

6) I detached the small condensation hose and unscrewed the cap at the bottom of the exhaust pipe.
I had paper towels under to capture the water.

7) There was a significant amount (about 16oz cup ) of caked aluminum oxide and gunk. I cleaned with garage towels the bottom of the exhaust pipe

8) I attached the 3 feet large hose at the bottom of the exhaust pipe with a clamp and the other end going into a 5 gallon bucket

9) I used a garden hose with a spray to wash the inside of the heat exchanger with hot water.
Took 30 gallons until the water became clear.

10) I connected a shop vacuum the large hose and sprayed more water on the exchanger ;
I'd say another 5 gallons. water was muddy in the vacuum reservoir .

11) Took a camera into the heat exchanger and it was quite clean.

12) I waited 3-4 hours for the exchanger to dry , reconnected everything, filled the condensation trap with a bit of water and fired up the boiler

Bottom line:

It's critical to do a period wash of the aluminum heat exchanger. Every 2-3 years at least.


Note for HVAC professionals:
I took photos and videos . I will jokingly do 'told you so' with the few HVAC companies and the local supplier shops I work with. All told me, nah no need to 'wash' boiler insides.
I even asked the company that changed my heat exchanger to lend the guy (which did a very good job at the time) for 1/2 day to work for me .
In my case I did not really want to spend 4 hours of hard labor in tight spaces monkeying with my boiler.
I am an engineer comfortable with electronics , pressured and burning or freezing systems so the physics and the mechanical parts were not difficult for me.
I would say the wash can be done by a DYI enthusiast with proper preparation.
But I wish the HVAC companies would step up and offer the wash as a service.
A photo of the gunk will likely convince any homeowner to fork the cost, which can be 3-4 hours of labor plus the gaskets .

EBEBRATT-Ed

@cas1717

I am sure anyone on this site who works on those boilers will be happy to have your insites. most companies are lazy. I have had people tell me that there is no need to clean the HX on MOD CON boilers as the condensate will "wash it out"

We all know this is not true.

The company I used to work for installed some Utica condensing boilers and they worked well. I don't know how many they sell but we don't seem to hear a lot about them on this forum and I don't know if that is a good thing or not.

Does that mean they run well and are trouble free or thy don't sell many?

Aluminum heat exchangers were very popular Buderus (now Bosch) used to use them and there were others.

Some aluminum HXs failed due to water quality.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1900196#Comment_1900196

i believe you also need to maintain inhibiter in the water side on aluminum hx boilers.

cas1717

@mattmia2

My understanding is that inhibiter or any treatment of the water side in an aluminum HX is needed only when antifreeze is used.
It happens I researched the water topic extensively when my expansion tank went bad twice within 1st year of installation long ago .First time the water was a muddy mess and the membrane in the tank failed because the original installer did not clean the conduit under the heated floors and 2nd time the expansion tank developed a pinhole from manufacturing defect (freak bad luck).
I had to read the technical specs and manufacturer design documentation of boiler and indirect water tanks.
Local HVAC companies were helpful to replace stuff but obviously would not spent hours diagnosing.
Turns out that all manufactures of fancy ModCons boilers use the same components (blowers by a company in Germany , the fancy MBCA control boards from Czech Republic, HXs are also shared , pressure sensors, lcwo boards,gas valves from honeywel ) so technical literature can be located if you look where the boiler manufactures buy from. The fancy ModCons are an infestation from Europe where the clean air laws are a real thing and the cost of energy is expensive relative to earning power. The US manufactures never really figured it out and most ModCons are installed with a thousand unused features in expensive households who will fork 5k to 10k extra for a 'green' boiler ( not really realizing savings are less than 100$ in gas per year).
I'm yet to find a HVAC company that will program boiler parameters (just ask to tune to match the outside sensor temperature curve and see how the technician looks at you :-). They are really afraid to touch the control boards in ModCons for good reason as , aside from the engineers who build the thing on contract before going into manufacturing, nobody in technical support at the manufacturer truly understand what each parameter does and how they work together .
I went sideways, but to come back to the water topic, I will recap what I learned :
When the aluminum HX is in a installation where the closed loop does not need antifreeze then use only
clean tap water in the circuit. If your town lets you drink the tap water then it is more than safe :-) for the aluminum as well.
The friction of the water moving thru the pipes will bring the water in chemical balance within the system (iron will rust a coating, aluminum will oxidize a coating, plastic is neutral), without the need of any other treatment.
Close the fresh water intake and only feed when pressure drops below the pressure for your installation ( typically 12-15 psi in a house, higher if tall structures). If pressure drops more than 1psi per year investigate for leaks. You can check every year that the water remains clean using the valve at bottom of HX since that is likely the lowest point in the circuit . If water is not cleanish (bit a color is very normal), purge and go figure why the closed loops get dirty.


Lots more information on aluminum HX in .
https://forum.heatinghelp.com/discussion/comment/1131955#Comment_1131955?utm_source=community-search&utm_medium=organic-search&utm_term=aluminum+hx
https://forum.heatinghelp.com/discussion/comment/1095602

mattmia2

https://forum.heatinghelp.com/discussion/comment/1900421#Comment_1900421

That discussion pretty specifically says aluminum boilers require inhibitors in the system fluid.

GGross

https://forum.heatinghelp.com/discussion/comment/1900421#Comment_1900421

I am not sure your level of proficiency but basically everything you stated in this comment is untrue.

EBEBRATT-Ed

I saw an aluminum boiler (I can't remember the brand) that had a 1/2" hole eaten through it and it was only 2 years old. They replaced it (maybe under warranty) with the same boiler and in 2 years that one was also shot.

How could that be possible?? LOL😊

We were called in for a second opinion, and we told them to get a water treatment guy in and replace the boiler with something else.

But they put the same boiler back in again because it was "cheaper"

mattmia2

when i was looking at mod con's i looked at WM's modcon and decided on something else when i saw that the hx was aluminum. it came with a bottle of inhibitor and required that you maintain it for the warranty.

EBEBRATT-Ed

We did a lot of Buderus back in the day (now Bosh) never had an issue but that was years ago.

cas1717

I was not correct to say "inhibitor or any treatment of the water side in an aluminum HX is needed only when antifreeze is used".

Inhibitors must be used when pH of water is out of range.

In my case, town water is at 7.4 pH within the Utica parameters and my installation does not need inhibitor. I have a hydronic loop with no need for antifreeze and chemically stable pipes: flexible plastic , few steel pipes around the boiler , the stainless indirect and copper in the air handlers.

Excerpt from the Utica addendum on WATER TREATMENT for an installation without antifreeze: https://uticaboilers.com/wp-content/uploads/2022/02/2444.pdf

"Verify water used to fill system meets these requirements:
System fluid pH maintained between 7.0 and 8.0.Maintain water hardness below 7 grains hardness.Filling with chlorinated potable water is acceptable. DO NOT use inhibitors or other additives that are not listed at the end in this addendum. Pro-Tek 922 Inhibitor may be used to adjust the pH level of the hydronic system.

Continuous addition of make-up water will constantly add oxygen to system. Eliminate
all system leaks. Operation of this boiler in system containing significant amounts of dissolved oxygen
can cause severe heat exchanger corrosion damage.This boiler is not designed for use in systems containing regular additions of make-up water. Regular additions of make-up water may cause severe heat exchanger damage. An unseen system leak will become obvious if boiler pressure decreases when make-up
valve is closed
"

My understanding is that Utica designed the aluminum HX to work with town water as adding inhibitor and measuring pH every time water is added in the inside boiler loop is not practical.

Bottom line, generally town water is fine as most towns maintain their water in the 7.2 to 8.2 pH range to protect pipes . But everybody should check.
There are various websites, one is https://www.homewater.com/water-quality-report