OldSalt
Member
(I hope this is the correct forum in which to post this. If this should have been posted to "Plumbing Forum, Professional & DIY Advice", please advise.)
I've had a long term struggle with a Rinnai Tankless hot water (RUR98iN) heating system I had installed in my new house. I have a problem with cold water in the hot water line, and intend to replace the gate valve separating the cold inlet with the hot water recirc return, plus replace a water filter at the main with a y-gate or y-screen filter valve, and would like advice on this before I dig back into my system. I'll post the questions first and the long-winded details and pictures after.
Questions:
1) I am using spring-loaded check valves (i.e. between cold water inlet and main, and between warm return and cold water inlet. Should I be instead using Swing check valves?
2) I selected the spring-loaded valves because I understood that the swing-check valves must be mounted horizontally, but that spring-loaded valves could be mounted at any angle. Does the mounting angle similarly effect spring-loaded valves, i.e. is that possibly why the valve malfunctioned? (I know that grit in the line could also foul the valve, holding the ball open, but that might account for lukewarm water, not ice cold for 10-15 minutes.) I mounted mine vertically because I had limited horizontal separation between the hot water inlet, the return, and the cold water inlet lines.
3) The y-strainer brass valves I've reviewed are fairly pricey. Plus, the poly valve I reviewed exceeded the PSI spec of the brass valve (e.g. max 150 PSI versus 125 PSI). On one hand, I sleep better using brass, but on the other, I over-spec everything, and maybe the poly y-strainers are better for this purpose. How much experience do you folks have using the poly strainers (example Banjo LS075-40 Polypropylene Y Strainer), and are they reliable? What size mesh screen should I be spec'ing for this (the Banjo strainer has a 40 mesh)?
Issues and history:
1) Original plumber installed it as a "cross over" system, rather than through the dedicated recirculating hot water line. He also left the switches set the default. He admitted he didn't have the background on the system, and said call Rinnai to figure out the dip switch configuration. I read the manual and figured out how to activate the system. It worked "so so". It took 10 minutes to run the re-circulation cycle to fill the hot water line and get "always hot" water in the faucets.
2) I read the schematic and understood that to configure a the system to run in a dedicated configuration, I needed to add (a) check valves on the cold water inlet line and the main, and between the cold water inlet and the recirc hot water line, add (b) an expansion tank, and (c) configure the dip switches. Result: The recirc cycle took too minutes. (Note: We can time the water heater to turn on and off to keep the water in the line hot, but we simply activate recirc when we use the hot water. We're using propane and it's cheaper - VERY cheap that way.)
3) We had a problem with what seemed like cold water blocks when activating the shower. The minimum GPM demand required to activate the WH is 1 GPM. The MOEN shower head with restricter was rated at 1.8 GPM, but with the city water 53 PSI, it was putting out less than 1 GPM during the test. I removed the restricter, got a full 1.8 GPM, and (seemingly) resolved the problem.
4) We had a problem with recirc shutdown, with WH alarms indicating a blockage. We found rock chips slightly bigger than a grain of sand in the WH filter, and had to clear the WH filter screen weekly. I added a whole house filter on the main to solve the problem. The city water delivers 53 PSI to the main, and with the filter, it is reduced to 49 PSI. Rinnai requires a minimum 50 PSI for the RUR98iN, so we're bubbling along at minimum water pressure for operations. However, there is still sand like debris building up in the filter every few weeks. That plus the PSI is the reason to switch to a Y-strainer to screen out these particles.
5) We're still getting the cold water blocks at a bathroom near the end of the hot water re-circulation lines, which is the current problem. It impacts all "downstream" faucets past that bathroom. After the recirc cycle completes, we flip on the shower and adjacent faucet (to ensure the hot water tank switches on), and pray. The water is normally hot, sometimes a bit cooler, and occasionally, starts hot and turns cold within about 20 seconds. I also cleaned out the shower head to ensure adequate flow. However, upon successive events we were still getting cold water 10 minutes after flushing the cold water block by opening all downstream faucets. There was simply no way there could be that much cold water in the hot water line due to a simple cold water block. Even stranger, the bath faucet and shower branch off the same hot water line, yet there was ice cold water coming out the faucet and hot water from the shower. Turn off the faucet, and the shower goes cold!
(These aren't all the issues I've resolved, only the relevant ones to the current problem.)
Conclusion: I ASSUMED that there was no way cold water could feed into the hot water line unless my error prone plumbers cross connected hot and cold lines somewhere (perhaps the third, "soft water" line at the sink). After a couple of weeks of thinking about this occasional (pain in the tail) issue, it dawned on me that the check valve was sporadically failing. Plus, all the problems are occur near the end re-circulation loop (where "hot" becomes warm return; hot water runs counter clock wise within the house).
I'm also wondering what kind of damage this could cause to the Rinnai unit. The hot water taps are open for 10 minutes, cold water is flowing from those taps, yet the Rinnai unit his fired up and heating (i.e. the "flame" icon is displayed). If cold water is backflowing into our tap, not much cold water can be flowing "forward" into the Rinnai. I know that the Rinnai has safety devices built in, but this can't be good for it.
Pictures If I had installed this system new, it would have been "prettier". After the original plumbers installed it, my retrofit is pretty ugly. (Note: the water tap below the middle return line comes out of the wall, i.e. it's directly connected into the return line unseen in this picture.)
I've had a long term struggle with a Rinnai Tankless hot water (RUR98iN) heating system I had installed in my new house. I have a problem with cold water in the hot water line, and intend to replace the gate valve separating the cold inlet with the hot water recirc return, plus replace a water filter at the main with a y-gate or y-screen filter valve, and would like advice on this before I dig back into my system. I'll post the questions first and the long-winded details and pictures after.
Questions:
1) I am using spring-loaded check valves (i.e. between cold water inlet and main, and between warm return and cold water inlet. Should I be instead using Swing check valves?
2) I selected the spring-loaded valves because I understood that the swing-check valves must be mounted horizontally, but that spring-loaded valves could be mounted at any angle. Does the mounting angle similarly effect spring-loaded valves, i.e. is that possibly why the valve malfunctioned? (I know that grit in the line could also foul the valve, holding the ball open, but that might account for lukewarm water, not ice cold for 10-15 minutes.) I mounted mine vertically because I had limited horizontal separation between the hot water inlet, the return, and the cold water inlet lines.
3) The y-strainer brass valves I've reviewed are fairly pricey. Plus, the poly valve I reviewed exceeded the PSI spec of the brass valve (e.g. max 150 PSI versus 125 PSI). On one hand, I sleep better using brass, but on the other, I over-spec everything, and maybe the poly y-strainers are better for this purpose. How much experience do you folks have using the poly strainers (example Banjo LS075-40 Polypropylene Y Strainer), and are they reliable? What size mesh screen should I be spec'ing for this (the Banjo strainer has a 40 mesh)?
Issues and history:
1) Original plumber installed it as a "cross over" system, rather than through the dedicated recirculating hot water line. He also left the switches set the default. He admitted he didn't have the background on the system, and said call Rinnai to figure out the dip switch configuration. I read the manual and figured out how to activate the system. It worked "so so". It took 10 minutes to run the re-circulation cycle to fill the hot water line and get "always hot" water in the faucets.
2) I read the schematic and understood that to configure a the system to run in a dedicated configuration, I needed to add (a) check valves on the cold water inlet line and the main, and between the cold water inlet and the recirc hot water line, add (b) an expansion tank, and (c) configure the dip switches. Result: The recirc cycle took too minutes. (Note: We can time the water heater to turn on and off to keep the water in the line hot, but we simply activate recirc when we use the hot water. We're using propane and it's cheaper - VERY cheap that way.)
3) We had a problem with what seemed like cold water blocks when activating the shower. The minimum GPM demand required to activate the WH is 1 GPM. The MOEN shower head with restricter was rated at 1.8 GPM, but with the city water 53 PSI, it was putting out less than 1 GPM during the test. I removed the restricter, got a full 1.8 GPM, and (seemingly) resolved the problem.
4) We had a problem with recirc shutdown, with WH alarms indicating a blockage. We found rock chips slightly bigger than a grain of sand in the WH filter, and had to clear the WH filter screen weekly. I added a whole house filter on the main to solve the problem. The city water delivers 53 PSI to the main, and with the filter, it is reduced to 49 PSI. Rinnai requires a minimum 50 PSI for the RUR98iN, so we're bubbling along at minimum water pressure for operations. However, there is still sand like debris building up in the filter every few weeks. That plus the PSI is the reason to switch to a Y-strainer to screen out these particles.
5) We're still getting the cold water blocks at a bathroom near the end of the hot water re-circulation lines, which is the current problem. It impacts all "downstream" faucets past that bathroom. After the recirc cycle completes, we flip on the shower and adjacent faucet (to ensure the hot water tank switches on), and pray. The water is normally hot, sometimes a bit cooler, and occasionally, starts hot and turns cold within about 20 seconds. I also cleaned out the shower head to ensure adequate flow. However, upon successive events we were still getting cold water 10 minutes after flushing the cold water block by opening all downstream faucets. There was simply no way there could be that much cold water in the hot water line due to a simple cold water block. Even stranger, the bath faucet and shower branch off the same hot water line, yet there was ice cold water coming out the faucet and hot water from the shower. Turn off the faucet, and the shower goes cold!
(These aren't all the issues I've resolved, only the relevant ones to the current problem.)
Conclusion: I ASSUMED that there was no way cold water could feed into the hot water line unless my error prone plumbers cross connected hot and cold lines somewhere (perhaps the third, "soft water" line at the sink). After a couple of weeks of thinking about this occasional (pain in the tail) issue, it dawned on me that the check valve was sporadically failing. Plus, all the problems are occur near the end re-circulation loop (where "hot" becomes warm return; hot water runs counter clock wise within the house).
I'm also wondering what kind of damage this could cause to the Rinnai unit. The hot water taps are open for 10 minutes, cold water is flowing from those taps, yet the Rinnai unit his fired up and heating (i.e. the "flame" icon is displayed). If cold water is backflowing into our tap, not much cold water can be flowing "forward" into the Rinnai. I know that the Rinnai has safety devices built in, but this can't be good for it.
Pictures If I had installed this system new, it would have been "prettier". After the original plumbers installed it, my retrofit is pretty ugly. (Note: the water tap below the middle return line comes out of the wall, i.e. it's directly connected into the return line unseen in this picture.)
