Boiler Piping Mystery

[Spock]

Let me preface this by stating that I’m not a professional HVAC contractor but have done several hot water tank installs, plumbing repairs and even rebuilt a Trane XV90 furnace. I’m a homeowner who’s not afraid to dive in and get in over my head.


I bought this house 7 months ago in the height of the insane real estate market. It was a bidding war to get it, I barely had time to get an inspection and one item corrected by the seller, the rusted gas lines. The furnace is brand new, the boiler isn’t. The main house is on a crawl space and is heated by forced air. The addition has a little connection to the forced air but has hydronics in the slab. The boiler is a Navien NHB-080. Before I started investigating the system, I fired it up, set the thermostat to 70 degrees and waited. The floor temperature was 59 degrees and after an hour it was still 59 degrees. Ok, something is wrong. All the valves are open, pumps Are running and the supply valves are open.


Not having any experience with these systems, I called a Navien boiler dealer to inspect and clean the system. He said the system is plumbed wrong. I have 3 pumps and only need 2. He said the flow was incorrect. He quoted me $3K to replumb it and $9K to replace it. Professionals are worth their money but I’m kinda short on money right now.


So, I dived into the Navien manuals, YouTube and every Hydronics website I could find (including this forum). Based on everything I’ve read and watched, I’m going to attempt to replumb the beast myself. I have a few questions that I can’t find answers for.


There is a Zurn ZW1070XL thermostatic mixing valve in the piping. I know what those are for in DHW systems but why is it in this hydronics system? Can’t I just regulate the temperature coming out of the boiler? They have the supply side going into the hot side, the return going into the cold side a T with one side going to the system pump back to the boiler.


The make up water connection is connected to the output side of the Navien manifold. Most set ups I’ve seen have the make up water connected between the expansion tank and the air separator. Even the Navien manual shows it there. My plan is to move it there with the Webstone expansion tank installation valve.


They reduced the pipe size coming out of the Navien manifold and then out of the air separator. Shouldn’t the system be one size? I know the size going into the floor manifolds are 1 inch but the Navien manifolds are 1.5 inches. What size should I run all the pipe? Upping the pipe size won’t be an issue if necessary. I will have to change the pump manifolds to accommodate a large pipe though.


This system, as it sits now, has no drain or fill connection as I have seen on other Navien installations. The plan is to add those.


Pictures are below. Any other thoughts?

Thanks

 

[Fitter30]

Lets not worry about corroded fitting and reduce size pipe for now. First pick make up water for system valved off. Is there a gage should read 10lbs. Can't follow the piping pics are to close for me. All heat emitters radiate floor? Backup take a few more pics from different angles. Any notes how long the loops are?

 

[Sponsor]

 

[Spock]

Yes, the system is off. Boiler is unplugged, water is off. There are no gauges on the system other that on the manifolds for the PEX pipe going into the concrete slab. Both gauges are broken, I plan to replace them. There are 3 loops and I have no idea how long they are. The system was installed in 2014. My one concern was the condition of the PEX in the slab. If I invested $3K to fix this and then found out that the pipes in the slab were bad I'd be a bit upset. If I can invest a few hundred dollars to fix this myself and the piping is bad, it's not as bad. I've attached one more picture, it's hard to get in there with the water tank and the washer and dryer next to it. I'm thinking of doing a flush of the in floor pipes to make sure what goes in comes out and to give them a cleaning before I start the system back up.

 

[Fitter30]

Pump under boiler line runs down to the left down to floor heat header?
Line from far left pump is that from another floor heat pex header?
#8 pic out of 9 that line is capped?

 

[Spock]

Pump under the boiler line runs down to nowhere. It comes off the main supply line with a T, goes down to a 90 pointed to the wall, hits the wall, turns left, switches from copper to PEX and then the PEX is capped with a sharkbite cap. Probably planned for future expansion or DHW? In either case I was going to take it out.

Far left pump is the only pump to the PEX header. It gets it's feed from the mixing valve, output goes over the return line an then down to the header.

I don't see the third valve. I see that each pump has a pair of valves, there is the gas valve and the valve on the Navien manifold. There is the Zurn mixing valve in there too.

 

[Fitter30]

Pump off the zurn valve do want to keep it?

 

[Spock]

Yes, that one should stay, it's needed for the boiler output to the header. Just don't understand the need for the Zurn valve. Would like to make this layout simpler if possible by taking it out and regulating the temperature with the boiler.

 

[Fitter30]

What type of heat emitters do u have? See might be floor heat, how many zones what types?

 

[Spock]

This is in floor hydronics heating, no emitters. No zones, 3 loops all one zone.
I got rid of the Zurn valve and a few pieces of pipe. I added a drain for the system. I have to move one pump (system pump) and close the whole thing up. Next step will be a bit of rewiring as I discovered that the boiler pump is wired into the Navien boiler incorrectly. At the same time, the system pump and the thermostat can be wired into the boiler also. This should eliminate the Caleffi Z-one Relay box.
After all that, time to turn on the water, check for leaks, bleed out the air and wake up the boiler. Hopefully it and the pumps run.

 

[Fitter30]

Radiate floor runs 5-10* over thermostat setpoint depends on type of floor coverings. Wood 85* tops.

 

[Spock]

The Zurn was (my guess) left at the factory temperature outlet of 115 degrees. My plan was to set the boiler to the same temperature. I was going to set the thermostat at 70 or 72 because they put carpet in the rooms with the floor heating and it has very, very thick padding. Should I lower the boiler temperature?