On-Demand tankless water heater mystery
I just had a Rinnai tankless water heater installed in place of an old conventional tank. The installation is in the basement of a hillside home, about 20 feet below the living area – in the exact spot where the previous tank was.
The hot water seemed to be working for a few days. I took a couple of decent showers in the first two days. But on the third day, the water ran cold during the shower; I quickly got out to see if anything else was running – nothing (the house is occupied by only two people). The next day – another cold shower – the only way I could get hot water was to run a couple of other faucets at the same time. Today, a buddy of mine helped me check out the unit while I ran each faucet in turn. ‘most’ faucets in the house triggered the heater. Reducing the faucet ‘demand’ (turning down the flow) resulted in the flame burning lower. I turned on the washing machine, which starts on a very low flow as it flushes the soap, and the burner was on even lower – one row only. But when I turned on my shower, the burner did not kick in at all. I removed the head of the shower in case it’s ‘low flow’ restrictor was an issue, but even without the head, the heater did not kick in. Turning on any other hot faucet nearby triggered the heater, and the shower ran hot. Yet this shower ran hot on the first two days (thought it did take a LONG time to run hot).
Another observation – while doing the dishes the other night, with the hot water on full, the water ran cold after maybe 5 minutes.
I’m going to talk to Rinnai and the installer, but I’m at a loss to fathom what could be going on here!
Replies
Do you have the remote installed? It might give you some useful info for diagnosing this.
One of the quirks about tankless heaters is that there must be a certain minimum flow to turn the units on. It is possible that during or shortly after the installation some dirt in the piping broke loose and lodged somewhere, restricting the flow or lodging at the flow sensor.
"I removed the head of the shower in case it's 'low flow' restrictor was an issue, but even without the head, the heater did not kick in. Turning on any other hot faucet nearby triggered the heater, and the shower ran hot. Yet this shower ran hot on the first two days (thought it did take a LONG time to run hot)."
Did you test the flow rate of the shower? How long does it take to fill a gallon bucket compared to the kitchen faucet that has no trouble triggering the burner? It might be that some debris has lodged in the shower control valve, restricting flow just enough to cause the problem.
After a room addition some years ago, my Moen shower control would no longer deliver enough hot water. When I took it apart, I found wood chips in the valve. They apparently fell into an open pipe before it was sweated back together during remodeling work.
I did test the flow rate, and - even without the head on - the shower only delivered 0.5 gallons per minute, which is a problem. I maybe facing a plumbing issue on that front.
I tested the other faucets, and they all delievered upwards of 2 GPM, well above any limit. Some delivered 5-6 GPM. So it still does not make sense that the kitchen sink ran cold when it was on 'full'. But I guess I need to deal with this as a multi-faceted problem.
Question - I contracted a licensed plumber to do the installation; I did not acquire the heater separtely and pay him to install it, and I did not specify the unit to be installed; I paid for a 'service'. IF it turns out the unit is defective, who's responsibility is it to work with Rennai to identify and resolve the problem, and to pay for the replacement (should it be necessary)?
From what you describe, I don't think the Rinnai unit is defective. Your shower is too restricted to trigger it. The plumber who installed your inline water heater may be responsible for whatever has blocked the shower line, but since you did not notice a lower flow rate in the shower immediately after the install, I'm guessing that the blockage was there all the time and the tankless has just made you aware of it.Is the shower flow restricted for both cold and hot? If so, the blockage is beyond the valve. If just hot, it could be in the valve or anywhere between the shower and wherever the line splits off from the line to that nearby lavatory that does deliver enough flow.Likeliest solution is to pull the shower cartridge (or stem, as the case may be) and look for damaged "o" rings or other debris clogging it. the kitchen sink may be on the end of a long large line, leaving a lot of cold water to be flushed through before you get any hot.BruceT
Edited 7/10/2009 2:26 pm by brucet9