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has anyone changed a diaphragm on the water valve of a Aquah 16L tankless water heater?

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posted 5 years ago

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Before we call our plumber I thought I would ask here...
this is the link to the water heater
We are fairly certain the problem has been the diaphragm. The water heater has been in use for four years and our water has a lot of scale even with a whole house filter preceding the water heater. The trouble shooting symptoms all pointed to that.

We have the new diaphragm and the Aquah guy says we don't need a plumber, just take off the water valve. Well it is not at all that straight forward...there are lots of things to disconnect, more than George has told us and he does not have a schematic...he says for us to call him for more help.....or to have the plumber call.

Steve is good at things like this but it looks like he would practically have to take all of the innards apart to get the water valve out and we are wondering if there is some other approach that is not apparent?

I'm somewhat annoyed that a part like that would come with no instructions?
This is the 'water valve assembly' that needs to come off of the heater and be opened up to replace the diaphragm

https://aquahstore.com/catalog/product_info.php?cPath=25_39&products_id=98

I've probably attached too many photos

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"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
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thomas rubino

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posted 5 years ago

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Hi Judith;
I have not changed the diaphragm on an Aquah, but I did on my Paloma PH -6 . Once you have access to the valve its simple, and straight forward. Getting too the valve is the knuckle skinning part.

Yours looks very similar. Mine has a standing pilot light, so no wires at all. I have no clue what the larger three black wires are coming from the top to the left or, if they are wires at all.

From what I can see, the yellow line is the propane regulator. It will need to come off. (sounds easy right... I hope/ but doubt it will be) After it is moved aside. The silver up pipe will need unscrewed/removed.
At that point it may??? be possible to leave half the cold water valve attached. Unscrewing the cover leaving the back in place??
If not, it appears that not to many more screws need come off, to get it free of the frame.
Once you have it in hand, installing the diaphragm is nothing.

Sorry I don't have an easy fix idea for you. Mine looked daunting until I started... then as each part came off the next would be apparent how it came off.
I'm confident that Steve can do this. Take pictures as each part is removed.
I mean after all, he is not building a RMH ... so no rocket science needed :)

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Gerry Parent

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posted 5 years ago

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Judith, I havn't replaced a diaphragm on your model either but have on our tankless Bosch heater. On ours, the diaphragm is located right at the joint where the two halves of the water valve assembly (WVA) come together.

Another take on Thomas' take-apart-tutorial based on your photos:

Be sure to check with step 4 first before continuing...

1)Turn off the propane, water and possibly power breaker to the tank.
2)Drain the water out of the tank by opening the drain valve on the WVA
3)Disconnect the copper line going to the WVA (on the right side)
4)Remove the 5 phillips head screws/bolts that hold the two halves of the WVA together (assuming you can access them all ?)
5)You may not have to disconnect the cold water inlet line which is PEX line and can flex somewhat, but at this point, the two halves of the WVA should separate and that's where the bladder should be to replace. Good luck!

EDIT: You mentioned scale. Have you checked the pre-filter to see if its clogged? If I had to guess, I would say it is located on the brass stem where the water inlet (the blue PEX line) is attached to. It is usually a long tube filter that is kinda wedged in there and is a little tricky to pull out.

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thomas rubino

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posted 5 years ago

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Good point Gerry!
Mine has a small screen pushed into the cold water side. It plug's up and then heater operation becomes erratic.
It still works but if you turn down the hot valve a touch to much... it will shut off. No fun while in the shower, where the cold water side is in the lower 30's all year long.

Judith, I know you have a prefilter, but you could still have another at the heater... worth checking before you dive in.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
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Judith Browning

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Thank you both!

For some reason the Aquah guy directed us towards the diaphragm...Steve had originally asked him about the filter/screen on the incoming water.

Will check that first.

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

Judith Browning

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Location: Ozarks zone 7 alluvial, clay/loam with few rocks 50" yearly rain

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posted 5 years ago

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4)Remove the 5 phillips head screws/bolts that hold the two halves of the WVA together (assuming you can access them all ?)
5)You may not have to disconnect the cold water inlet line which is PEX line and can flex somewhat, but at this point, the two halves of the WVA should separate and that's where the bladder should be to replace. Good luck!

'assuming you can access them all' ...and that is the problem. It looked like changing the diaphragm would be just that straight forward but the screws were impossible to access without removing many other things.

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

Gerry Parent

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posted 5 years ago

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Sometimes if there is enough room to accommodate one of those small phillips head bits (from a multi-bit screwdriver), then with a pair of pliers grab onto it an turn it, can work too.
I have one of these tools that has gotten me out of trouble more than once that look like this:

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thomas rubino

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Hi Judith;
I'm hoping you find a dirty inlet screen.
I'm curious what the complaint is about your heater ?

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Judith Browning

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Location: Ozarks zone 7 alluvial, clay/loam with few rocks 50" yearly rain

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thomas rubino wrote:Hi Judith;
I'm hoping you find a dirty inlet screen.
I'm curious what the complaint is about your heater ?

At the moment, for it to kick on at all, we have water flow turned as low as possible and the gas itself up a little from what was normal for years.

In order to get hot water at the kitchen sink we have to have another faucet running. The washing machine hot kicks on and so will the bath tub on their own because they have a heavier water flow. To take a shower and keep the hot flowing we have to have the sink running at the same time. We're wasting a lot of water at the moment. Until we figured this much out, the hot was shutting itself off during a shower and we couldn't get any hot to the sinks....I'm probably not explaining it very well but we got to this point through a lot of adjusting and testing different combinations.

The first thing Steve asked about at Aquah was the inlet screen and for some reason the guy thought we needed a new diaphragm.

We also had the cover off and cleaned all the dust, etc out, checked the burners, replaced the 'D' cells, ran vinegar through the system...

Until the last few months, it has worked great and steady at a certain setting. Over four years we had pumped vinegar through it twice and not done the other cleaning, so it's definitely time to catch up with maintenance.

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

thomas rubino

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Well its worth a look at the screen. From your description its hard to say, it very well could be the diaphragm.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Judith Browning

Posts: 9168

Location: Ozarks zone 7 alluvial, clay/loam with few rocks 50" yearly rain

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Checked today and unfortunately, the inlet screen was clean...we were hoping for some glaring gunk there, but no.

onward...

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

thomas rubino

rocket scientist

Posts: 6524

Location: latitude 47 N.W. montana zone 6A

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Hi Judith ; Thanks for the update.
I thought about your heater, just this morning! Wondering if maybe a screen cleaning worked for you! Bummer that it didn't!
I'm still sure Steve can do this. Like any mechanical job , it looks bad , BUT as you dig in, things generally become clear how to proceed.
Good Luck! Let us know when you get it working well again.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Gerry Parent

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Judith Browning wrote:The water heater has been in use for four years and our water has a lot of scale even with a whole house filter preceding the water heater. The trouble shooting symptoms all pointed to that.

The scale you mentioned keeps coming back to me. Have you checked your whole house filter lately? It could be that its getting plugged and slowing the water flow enough to not trigger the heater anymore or the heater itself is getting a scale buildup and doing the same.

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Purity Lopez

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"At the moment, for it to kick on at all, we have water flow turned as low as possible"

Judith. I have this water heater and also a pre-filter setup. Have you checked the incoming PSI on your water? The Aquah is designed to automatically shut off if the water pressure isn't high enough. When was the last time you checked your filters on the pre-filter system? Perhaps also, maybe there is calcification at some point in your pipes and the water pressure is different at different places in the house. I have 8.5 water here, and I have had to replace one tankless after another. I finally got so tired of having constant problems that I just disconnected them from the pre-filter systems and have them on their own dedicated pipe systems on 5 gallon propane tanks. In regards to the Aquah guys, they are really really nice, they helped me with a problem where I made a big mistake and they didn't have to help but went way out of their way to help me resolve the problem I created. That said, I seem to have communication problems with them whenever I talk with them. We never seem to be on the same page - LOL.

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Jerry Sledge

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posted 5 years ago

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Just for information, scale is from dissolved minerals in the water. It can't be filtered out. You would need a water softener installed to lower the mineral content in the water.

Had a similar problem with an old tank-less water heater.Home owner decided to up grade the heater. Wan not easy to change out the systems. Required replumbing to adapt the new heater.

Paul Deel

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Judith,
Just start taking things apart until you have the diaphragm valve in your hand. Then, and only then, remove the 5 screws on the cap. Be very careful when you take apart a connection made with bolts or screws because there is a fragile gasket in there that needs to be reused. I wet the gasket with plumbers grease or a silicon lubricant. Not too much, just wet it.
I have never had luck with vinegar to de scale the coils. Try a de scaler specially made for tankless water heaters. Home Depot and Lowes have them. also some tankless heaters must be plugged in and turned on for the modulating valves to open allowing the circulation of the descaler. Keep the gas off.
A phosphate feeder in the cold water supply may help keep the minerals in suspension as they pass through the coils. Some swear by the magnetic affect when two permanent magnets are bolted to the supply line. They are sold as a kit.
Another thing with tankless heaters is to set the temperature low and if possible shower with hot water only. We used to call them flash heaters and each person would set the temperature they liked when they showered.

Judith Browning

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Location: Ozarks zone 7 alluvial, clay/loam with few rocks 50" yearly rain

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Thanks everyone...

We change the whole house filter monthly...more often than recommended.

The heater has worked great for four years, until the last six? months.

We are adaptable so because we could keep it functioning with a few tweaks we're slow to fix although I know we are wasting water. The hot shower is still working as long as the sink faucet is running at the same time...and it used to work perfectly set at a certain level of gas and water flow according to the temperature of the incoming water, seasonally.

We have municipal water and really good pressure...that was one of the first things we looked into when we bought the water heater. I don't remember the numbers though?

The filter was good, we have the new diaphragm here ready to go but thought we would try the vinegar again and then backflushing through the diaphragm in case it is clogged and not worn out (stiff?). Have not looked into the commercial descaler stuff? Might need to....

Thanks for all of the input...very helpful!

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

leila hamaya

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well i have had a few different cheap/older tankless hot water heaters that had quirks....so possibly what i went through with one could be related. for me with one it was the pilot...where the small part that was where the pilot light went on got ??? clogged with funk ??? or something, and taking this off and giving it a long soak in some strong cleaner stuff my friend hooked me up with..."fixed" my old hot water heater...where it stopped going on and off.

well yeah, no idea if this is your issue, and maybe not since you say it's related to not getting enough pressure and having to turn the sink on...hmmm...but, worth a thought anyway...if it's not the pilot/gas line flickering. those hot water heaters can be finicky. i've used several and almost all of them did that every so often...which SUCKS when your showering and suddenly get cold...although it was usually ok and only doing that every once in a great while isnt bad.

leila hamaya

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one other thought, which may or may not be relevant, is that if you found out it is the related to the water pressure you could get a pressure tank. this would well cost money and be a chore...but i have also lived with really bad low pressure water and a finnicky tankless heater...and my landmate at the time got a pressure tank and this immediate worked out with the issues the hot water heater was having, cause it evened up and seriously upgraded the pressure.

Judith Browning

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hi Leila, great to hear from you! Haven't seen you around for awhile?

The water heater has a battery powered electric ignition so no pilot light and we've switched out the batteries so they are fresh.

The water pressure is fine, we checked it when we installed the heater and it's worked great until about six months ago.

thanks though!

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

leila hamaya

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yep, well worth a thought. stuff like that is always so tricky to figure out. best of luck.

and yeah i've been offline, working a lot, "gone dark" for a while! am getting tons of stuff done though...

Judith Browning

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Location: Ozarks zone 7 alluvial, clay/loam with few rocks 50" yearly rain

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checking here first to see if anyone has tried this:

1) Wash the diaphragm clean by pumping pressurized water though the water
outlet (hot side) into the water heater
What is not explained is if 'pressurized' water is just a faucet through a hose pressure? and if the water needs to be draining through another hose on the cold side while being run through the diaphragm?

We are having one of those series of breakdowns on 'stuff' so have not got back to this one as we can still get hot water.
Of course, the breakdowns are coinciding with company coming in a couple weeks

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

Judith Browning

Posts: 9168

Location: Ozarks zone 7 alluvial, clay/loam with few rocks 50" yearly rain

2563

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Tried a vinegar flush again....no change.
Will probably end up ordering the commercial stuff.
We are slow and it has not gotten worse so using it as is for the moment.

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

Judith Browning

Posts: 9168

Location: Ozarks zone 7 alluvial, clay/loam with few rocks 50" yearly rain

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Well, five years later...
It quit working all together soon after my last post.
I ran across the manual today and I thought I would look at it all again but am quickly losing enthusiasm.
We heat water in a kettle on the propane cook stove for dishes and bathing and certain hand washed laundry...the washer just uses cold.

The only time it seems a chore is when we have company but most who visit think we're nuts anyway and just enjoy the novelty

"We're all just walking each other home." -Ram Dass
"Be a lamp, or a lifeboat, or a ladder."-Rumi
"It's all one song!" -Neil Young

this is supposed to be a surprise, but it smells like a tiny ad:

A PDC for cold climate homesteaders

http://permaculture-design-course.com