Rinnai Combi 3-way Valve Siezing

babyak

I have a Rinnai E110CN model installed in both my residence and a rental property since 2017.  The issue is with the 3-way valve (Rinnai part 807000030).  Over time a scale is forming on the valve and it seizes up causing an issue with the heat, faucet hot water, or both.  I’m having to replace about 2 valves each year on both boilers.  I’ve also had to replace the actuator (Rinnai part 805000030) twice as the motors have burned out trying to move the seized valves.

Both homes are on the municipal water supply. Both have old cast iron radiators. 

Last fall I installed scale cutters (Rinnai part 103000038) on the incoming water line on both boilers as recommended in the E110CN combi-boiler manual.  These are essentially water softener columns with a compound that slowly dissolved the incoming cold water. Unfortunately they haven’t helped at all.  I also installed a Spirotherm Spirotrap on one of the boiler’s return line which also did not have an effect.  A couple years ago I flushed the radiators on both systems which also made no improvement. 

Rinnai has been less than helpful. They’re last communication just states the water pH should be checked on each system to verify it is within spec (no spec provided). They also said the systems may need to be flushed with something to remove anything that may be causing scale formation (no recommendations provided). After that they say there really isn’t anything else that can be done. 

One notable factor here is that I installed one of the valves at the tail end of last year’s heating season in early April (I’m in PA), but it failed in early October. So this means that virtually all water running through 3-way valve was from the incoming supply for hot faucet water. So I’m wondering whether flushing radiators or adjusting pH would really have any impact. 

I hope someone has some suggestions as I really don’t want to spend a lot of money on separate hot water heaters and make the boilers only for heating. Thank you in advance!

hot_rod

Doesn’t that valve just see the boiler water, switching from heat to DHW heat exchanger?
If so the water in the boiler must have a lit of scaling minerals. Take a sample and test hardness and TDS. The manual should tell you the allowable number for each. Generally under 10 or 12 GPG grains on hardness

Hopefully the boiler is not taking in additional fill water? That would indicate a leak in the system

Hydronic cleaners and conditioners could be added to “fix” the boiler water

Or drain, flush with a cleaner and add filtered, DI water
Yhise 3 way valves are very common on combis and should work fine for years with good water quality 

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_18_na.pdf