GE Merlin Reverse Osmosis Water Filter Problem Drain Water Stuck On, Never Shutting Off Solution & Other Useful GE Merlin Application Notes
Apparently it is a known problem that the Merlin RO tankless water filter gets stuck so that drain water is constantly running. Supposedly there is a product re-design in the works according to what I have read on the internet by the company that bought the Merlin RO product from GE. Note there is also a ~$500 housing available from a company in England of completely different design that uses the Merlin filters. Having owned a Merlin RO filter for several years I see that I too now have this problem, however I tried a repair I read on the internet and it seems to be working. First off this is a 2 part Merlin design problem. Merlin Design Problem Part One - Unlike other RO filter units that have an externally accessible automatic mechanism that shuts off the drain water when the output water is shut off, the Merlin has this mechanism buried inside where it can not be accessed without cutting the Merlin apart. Not good! Well there is a rubber valve mechanism inside and over time it dries out, and gets stuck easily. What I did after reading about the internet suggested repair was remove the filter from service, take the 3 filters out, spray silicone into Manifold hole of the top housing (about 5 oz), let it set for a few days, while every once in a while I would run hot water thru it. I made a set up which allows me to use a garden hose to the kitchen sink, then with the right adapters, into the Merlin without internal filters. I also put a shut off valve on the Merlin output that allowed me to stop the water flowing out of the Merlin. The idea is that this will create internal pressure to exercise and break free the internal stuck valve. Note that I accidentally was shutting off the drain valve water for a while. This turned out to be a good thing. This started an internal resonating vibration at the right water pressure (adjust the sink water handles to the right pressure until you hear vibrating). That vibration together with the silicone, I believe broke the rubber shut off mechanism free, allowing the silicone to coat it, and operate properly. Once I was able to operate the on off valve to the Merlin output and saw that the internal shut off was now working properly, I ran cold water for a few hours to flush out the excess silicone. This was the part I read from some good Samaritan on the internet. Note that running hot water thru a garden hose may soften the plastic and eventually burst the hose, especially if there are no internal cloth stiffener strands in the hose. This first design flaw seems intentional to force users to purchase a new Merlin Manifold every few years which is a $125 proposition. Not me! If the valve were user accessible like other RO filters, this would be about a $10 fix. Merlin Design Problem Part Two – This design flaw is two part as well. Part one of two, is created because of not having an external storage tank. The external storage tank gives back pressure when the output valve is shut off which pushes back and shuts off the drain water via the internal valve. GE Merlin solves this problem with the post filter. The special Merlin post filter has 2 parts inside. Part one is standard filter material, I assume charcoal, and a second empty space with a plastic bladder about the size of a ping pong ball. That bladder (air bubble) gets squeezed when the output is shut off by the internal water pressure which then acts like a pressurized external water tank. This system does work when new, and if you continue to use the correct Merlin post filters, you will never know the difference. Not me. I cut open my used Merlin post filter to discover that the internal bladder was broken, unable to create any back pressure. Together with not documenting any of this, this seems like another GE Merlin intentional design to force users to buy Merlin replacement post filters. Since I don’t like to be forced to do anything, I designed my own mini external tank and bladder to replace the wimpy Merlin design. I used a standard plastic RO filter housing with a partially inflated rubber glove to act as the bladder. Note that I shut down the third hole with one of those ¼ inch John Guest stopper “T” things. I also put a little piece of plastic tube inside from top to bottom ( angle cut at both ends to keep water flowing) to keep the inflated glove from cutting off the water flow. Come to think of it, you could probably use a partially inflated condom to form the air pocket which gets squeezed down to create the back pressure. Really you just have to keep the air from flowing out of the housing.
Dope! That only took me a few years to figure out. Now because my output water runs slower, and I am filling up a large 150 gallon tank, I tried adding a flow restrictor to the drain water. The idea was that since the output water was going slower, the drain water should be slowed too. Well what I found out was that adding that resistance to drain water (flow restrictor) caused the Merlin RO output to go up to about 50 ppm. Not good. So I took that off. Knowing that lead me to believe that slowing the Merling water output with the ¼” hose, is responsible for getting the output to 2 ppm. This may not seem important but 10 ppm output wears out the DI cartridges much faster than 2 ppm output. A DI cartridge will only remove a certain number of ppm before it does not work any more.
Joe
