anthonyc19
New Member
I have a 16 year old tankless water heater. It's in my laundry room in the middle of my ranch house. I perform routing maintenance on it (replace flame sensor, replaced fan motor, descale). I was getting random, inconsistent error code 10 (air supply or exhaust blockage) after the water was running for 10-15 minutes. If I turn off the hot water, it seems to reset and the hot water works again.
The condensation drain hose looked clogged, so I replaced that. No visible blockages in the roof exhaust. Still have error code 10 once in a while. It was due to be descaled, so I did that. When descaling with vinegar, the outflow started strong, then quickly slowed significantly. I thought the pump was compromised. Everything looked right. Supply valves were closed. Flush valves open. Unit plugged in, but off. Gas turned off, cleaned pre-filter. I let the pump run and descale for 90 minutes. There was a decent amount of sediment. I opened the water supply and flushed it out into my slop sink for 3 minutes. Checked and rinsed the pre-filter again (it was clean).
When done, I turned everything back on. When I used the hot water in my powder room (off kitchen), blue vinegar smelling water came out (the blue is from the vinegar reacting to the copper pipes). The hot water valve was closed when I was descaling. wondering if the valve is bad. there should be no vinegar in the pipes.
Then, I noticed that, when turning the hot water on in the kitchen, it was VERY cold, as if it was the cold water supply. That is still happening a few weeks later. The water is noticeable more cold when initially turning on the hot water and it takes longer to heat up. It seems as though the cold water supply is getting into the hot supply, but once the water heats up, it's hot as normal.
A few days later, I heard a loud hissing coming from under my kitchen sink. it happened for a couple minutes and went away. then it happened again and went away. Soon after, I started hearing a much quieter/faint hissing under my sink. I can tell it's coming from the hot water line because if i hold the line, the sound slightly changes. I am on a slab and feared that I now have a leak under the slab. this happened for a few days. I monitored my water usage and found that I was losing about 5 gallons per hour overnight when no one was using the water. I checked all toilet tanks and they are not leaking. Then, the sound went away and I was getting 0 water usage overnight for about a week. After a week of no water loss, the faint hissing sound under my sink returned. I am now losing about 9 gallons per hour overnight. I can hear the sound under the sink of my kitchen and under the sink of my powder room. They are close to eachother, approx 12'.
Something happened when descaling. I am really nervous that I have a leak under the slab, but it doesn't make sense that a leak stopped for a week and returned. I'm wondering if there is a mixing valve that is bad somewhere which is allowing cold water to cycle through the hot water.
Now, I have a small puddle forming under my water heater. it is from condensation dripping from the cold water supply pex pipes. I have been in this house for 16 years and never had this happen. There was also some water that appears to be condensation inside the water heater. Cold water must be cycling through.
I am scheduled to have a leak detection. Also worth noting that I still get error code 10 occasionally. I am hoping it's something other than a leak under my slab, but I can't figure this out.
