i'm in serious need of advice: all of this started with the water heater-it split down the back and started leaking like crazy and had to be replaced. that was done a week or so ago and shortly afterward the thermal relief began to trickle. (forgive me-this is the ball valve that has a tube sticking out of it-i'm an electrician and am not sure what all of the terminology is exactly-expansion valve? thermal relief valve? 125psi thermal expansion relief valve?) so i replaced the expansion valve. that was not the problem-it kept trickling. so i hooked a guage to a bib and found that the pressure went through the roof after a faucet was closed. somewhere around 120lb. i guessed that the regulator(i've heard it referred to as a prv?) was bad-so i replaced it. i tested for leaks and things were good so i turned it back on. it worked like a champ-i set it at 60 and called it good. it looked good for a while...til i realized the expansion valve was trickling yet again. the bib guage was at 140! i know i set the prv correctly-i adjusted it, turned on a faucet, adjusted it again and it held at 60. i'm ready to snap.:wall: any input would be great. i'm running out of things i can replace

I want to install a Paloma indoor 7.4 series tankless water heater. I would like to use the existing venting used with the conventional heater I'm replacing. It has a 3" galvinized sheet metal pipe to the ceiling at which point it is adapted to a 4" gsm pipe up through to the roof jack. I would replace the 3" portion with a double wall 4" pipe getting me past the ceiling joist. I really don't want to spend an additional 300 bucks on top of the cost of the new tankless for a venting installation kit if i don't have to. Will my idea work. Thanks Harryrdgrs