Rinnai requires multiple faucets to fire

Boomer3731

I have an outdoor R85 unit that, after sitting for 4+ hours, will not fire with just a single running faucet/fixture. After I can get it to fire with multiple faucets it will stay on with just one faucet running but when it cools down (4+ hours) it requires several running fixtures to fire again. I have replaced the flow servo unit, flushed the HX with white vinegar, and checked the cold water inlet filter for debri with no luck. Any suggestions?

Jack

Well, I thought I had this one cold...until you said you had replaced the servo. That unit should fire at .4gpm, 10,200 btu min and hold operation down to .25gpm. Are you getting any error codes? When you open a faucet, is the unit pre-purging and not sparking or does it just sit? Sequence is flow, fan, spark, fire and flame current. If the unit is not doing anything I would still say servo. Beyond that you get into the board, which is I think unlikely as I don't think it would be intermittent. Gas valve that is not opening until higher demand? Tech Serv is 888 746-6247.

rick in Alaska

Wire connections to servo? Maybe loose or crusty.
Rick

Mad Dog_2

Had that happen with one of those open spout
Lavatory faucets. Engineering said they needed a minimum of back pressure to fire. Mad Dog

hot_rod

Does it have a small paddle type flow switch that activates the process? If so, maybe something is causing that to stick?

Slimpickins

Actually the R85 has a .6 gpm activation rate and a 15,000 min. BTU load.
To find out if you have at least 15K BTU demand use the ol' GPM x 500 x temp rise formula.
If you have the MC-91-1 control, you can read GPM by holding down the Up arrow for 2 seconds and without releasing after 2 seconds, press the on/off button for a moment and then release both at same time. You will then get GPM's, there are no decimal points so if you're getting 4, that's .4 and if you get 15, that's 1.5 gpm.
You can check inlet temp if the unit is still not firing by doing the same sequence but using the down arrow and then the on/off button. Now you know your ground water temp (since your reading the outlet thermistor reading with unit not firing) so subtract that from your temp setting on control and you have the temp rise and you can use that BTU formula. If the number is below 15000, the unit will not fire and you can try raising the temp setting of control. Sometimes in southern climates you have to raise the temp settings in the summer with the high ground water temperatures. If you're checking the outlet temp and unit hasn't fired and it's in the 100's, you either have a dirty or bad thermistor and that's your problem.

Jack

Slim, you are correct! The .4 gpm flow didn't hit until the R94 was introduced. Thank you for the correction and my apologies for the incorrect specs.