Sorry if this is a bit long . . . Due to frequent power outages where we live, a few years ago I installed a Myson 325 propane tankless water heater in parallel with the electric tank that normally provides our house with hot water. As a back-up system it has been great though it has some quirks that would cause me to not want it as my primary source of heated water. Anyway, my main problem with it is the external pressure relief valve will start to flow if a hot water tap in the house is only opened just far enough to cause the burner to come on. Obviously the water in the coils is getting too hot under this circumstance (low demand) causing the excess pressure. To compound this problem, when the house tap is then turned off the flow at the pressure relief valve is now great enough to cause the burner to remain lit as the system thinks that a tap is still open somewhere. I have played around with adjusting the water flow metering valve and the gas thermostat adjustment screw but can't seem to find any settings that solve this problem. I thought the thermostat adjustment would adjust the burner but after tweaking it up and down I couldn't really tell what, if any, changes it was making to the system. The only way that I can get the pressure relief valve to stop flowing (other than turning off the gas to kill the burner) is to fully open a hot water tap at a garage sink near the heater thus greatly increasing the flow which cools the coils down significantly. Then by abruptly shutting the tap off the burner will shut down. So, I'm wondering what the solution to this problem is. Would an expansion tank on the hot water side help matters? Do I need a technician? The owners manual isn't the greatest and of couse in the trouble shooting chapter there is no mention of this type of problem. Advice anyone? Thanks in advance!

As I type this my 14 year old tanked water heater is being replaced with a Navien 240. My warranty is 15 years on heat exchanger, 5 years on parts and 1 year free labor. No requirement for an annual service. Additionally, the company installing the Navien has a policy that guarantees if, during the first year I have the Navien, I'm unhappy with it, they'll remove it, and fully refund my money. They said they've never had a customer claim that benefit. All of their customers are happy. Last year, when the state tax credit was in effect, they were installing 2-3 Navien units each week. Install rates have fallen off a bit since the state tax credit has been dropped. Interestingly, they're installing Naviens only in existing homes. They were also candid that, like other new technologies, there were some hiccups a few years ago that needed to be worked out. In their opinion, all problems have been resolved, and today the best, most reliable tankless units on the market are Navien and Eternal. I chose the Navien because the heat exchanger is stainless steel, not copper, eliminating the need for the periodic de-scaling required of other makes. And because it appears easy to operate...more so than the Eternal. I'm nervous at the change. And I'll post back here after I've lived with the Navien for a month. I've got house guests coming later this month, and it'll be interesting to see how it performs with lots of showers, laundry, dish drawer use, etc. I'm so pleased to hear that Rob is delighted with his new Navien.

Wow, thanks for all the good input. I didn't intend it to become a debate about solar, but found that interesting as well. I'm not familiar with the lease program that is mentioned. I'm looking to have an array installed that will be owned completely by me. I can get a 20kw system installed for about $60,000. There is a new Duke Energy program offering $1 rebate for each kw installed, so subtract $20,000. Then there are 55% state and federal tax credits, reducing the investment further to $18,000. The system should generate about $2,500 in energy per year (assuming 9 cents per kwh), resulting in about a 7 year payback. There is also potentially a benefit I can derive from depreciating the asset, but am not sure that is allowed, so need to check with my tax expert. I think the main different between now and before is the $1 Duke rebate. Without that, I agree the payback period would be too long (about 11 years), but a 7 year payback seems reasonable to me. There is always the possibility of repair costs in the first 7 years which could lengthen the period a bit, but the warranties on the panels at least are much longer than that. In any case, I think it is a worth a try. With regard to the water heater question, I agree that two heat pump units might be too many, as the one in the basement might be idle for long times, so am not considering doing 1 heat pump (for the upstairs which will get used daily, but shouldn't use more than 80 gallons per hour as there is only 1 shower), and then a gas powered tankless for the basement. We have natural gas that will be already piped to the house for the stove/grille. Any other thoughts or suggestions are welcome, thanks for the lively debate!

Hi Charles Ross Homes, Thank you for your thoughtful response. My home is a 1960 single story ranch situated in a Southeast Texas. All of the homes I have owned here have had the water heater (tank or tankless) in the attic. City code permits for this install location. Not all, but many, homes in the area have water heaters in the attic. I understand about the potential leak issues - we have water leak monitoring and emergency shutoff and water collection pan/drainage in place. My garage is detached and on the Northeast side of my property. It would take quite a bit of work and cost to move the water heater (and associated gas/power) to the garage. I could consider putting the Navien on an outside wall, but that would require it to be installed on my master bedroom wall or in an unprotected area. I don't feel it would help with the sound issue anyway and there is the cost issue as well. I think the Navien NPE-240A is just not a good fit for my needs and constraints -- given its operations and operating requirements. My last instant water heater was a Noritz - put in by the previous homeowners. I never heard it operating. I'm sure it made some sound but that sound wasn't loud enough to permeate to any of the living areas. They don't make that Noritz any longer. Do you have recommendations or suggestions for a "quiet(er)" tankless system? Thanks.