Is tankless hot water and on demand the same thing? When i bought my house i had the hot water on demand thingy and it kind of sucked. I got rid of it and replaced with an electric hot water heater which has been great.
The problems I had were that I kept having to get it cleaned because it was getting plugged up with lime scale incredibly fast. I'd loose water pressure until I eventually had no water pressure at all. Each cleaning was $800!! 6 months would go by and it would need to be cleaned again. I'm on top of my water softener but the well water here in the sourlands is just really hard I guess.
Other issue I had was that I was burning oil all year round just to heat water. Now I can shut my boiler off for 6 months. The additional electricity usage doesn't come close to the oil usage.
1. there is a
sacrificial anode for the tank which is supposed to go "first" - then be replaced before the salts attack the heating element and
nipples. you might need to make this part of your 3 month maintenance, unless #2.
2. make sure the inlet and outlet pipes are bonded together with a copper cable just above the water heater. if there is any electric ground finding its way to the water heater, it will create a current in the water, and it destroy it damn quickly. the pipes are insulated from the water heater with a dielectric coupling (unless #3), so the only way through is via the water. esp being electric.
3. make sure they used dielectric couplings, or the unit has built-in dielectric nipples. otherwise it is part of your electric grounding system (not good)
4. it may be cheaper to add a water softener, then to destroy you water heater. it will also save the dishwasher, washing machine, and faucets. don't soften the water to your ice maker, or primary source of drinking water, or plant water. it tastes crappy. at a minimum, soften your hot water. your clothes will thank you.
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other than low flow failure, what was wrong with your demand system? mine works great, other than exceeding its limits if someone runs the water, but then again, i have a well, so the input is also limited.