Asking for advice for combi boiler replacement and hydronic system upgrades

hilltown

fill valve and expansion tank set to 20#’s

Seasoned_Amateur

hilltown

that is what Rinnai wants those set to on a cold boiler

Seasoned_Amateur

These are during install earlier today before I started commissioning the boiler.

Seasoned_Amateur

hilltown

is that a heating expansion tank or a domestic expansion tank?

Seasoned_Amateur

I purchased the expansion tank from a radiant supply store, so I hope it's heating. But, I'm not sure how to tell.

Seasoned_Amateur

Bell and Gossett

hilltown

it should say working pressure on the label , usually a heating one is factory charged 12psi and a DHW is set 40psi

Seasoned_Amateur

The pressure gauge is reading 22#. The expansion tank is from my old configuration. I probably need to check and adjust the pressure on it.

Seasoned_Amateur

I'll get that expansion tank dialed in, but I'm guessing that doesn't effect my boiler pump not coming on.

hilltown

I would say fill it to the analog says 20psi, shut of the shutoff to the feeder/backflow and the boiler relief goes off still, Only a few reason for a boiler relief to go off, a bypassing water feeder, expansion tank bladder is shot and a coil or plate hex that is leaking domestic into the heating. The other side of this is all the water is cold because the gas isn’t hooked up yet.

hilltown

going to need to check power to that pump when it should be running,

Seasoned_Amateur

Expansion tank and pressure are both now reading 20#

Seasoned_Amateur

The gas is hooked up now, though it wasn't in those photos.

Seasoned_Amateur

I'll check to see if the pump is getting power.

Seasoned_Amateur

I pulled the terminal connector off of the pump. I ran the deaeration setting and checked voltage at the terminal clip. The pump is getting 120v, but it is definitely not spinning.

Seasoned_Amateur

The pump says it's thermally protected. I wonder if it needs resetting?

bjohnhy

That grundfos pump has a manual switch to go between 3 settings? You may check that the switch is not stuck between settings.

Which PRV is releasing? Boiler side or DHW side?

Seasoned_Amateur

Thanks, @bjohnhy . I did run the switch through the speeds, but no luck.

Seasoned_Amateur

@bjohnhy prv on the boiler side

bjohnhy

I get the impression the pump turned on when you activated DHW. And that's what caused prv to release. Now that you have the pressure better calibrated, hopefully that won't happen. Did you try it again, maybe pump on L1 to start?

What is the prv rating?

You're in Seattle area? Want me to stop by just for 2nd set of eyes?

GGross

fully open these valves you are possibly dead heading your pump and blocking it's ability to see the expansion tank

Once the boiler cools down check the actual static pressure of the system 20psi is pretty high for static pressure unless you are in a 3 story building with heating on the top floor. re adjust the expansion tank after if necessary, also you must fully remove the expansion tank from the system to check or adjust its pressure you cannot do thin while it is connected

Seasoned_Amateur

Thanks, @GGross. That photo was taken while I was still had a few pipes left to solder. All valves are full open. 20 psi is what Rinnai requires for this boiler. I think it throttles down below 15 psi. I didn't know that it's best practice to remove the expansion tank to set it's pressure. I'll do that.

Seasoned_Amateur

@bjohnhy I'm in south Seattle and would love a second set of eyes if I can't get a resolution with Rinnai tech support. That would be amazing. I'll let you know.

GGross

If you can post a current pic it would be helpful just in case you do not get a resolution

Seasoned_Amateur

Rinnai is sending out a new pump. Should be here in a couple days. They said they fully test units before they go out. Why this pump isn't working is a mystery. Hopefully, replacing the pump is simple…

GGross

a non working pump doesn't explain the pressure immediately blowing off the relief though, sure the boiler would reach its fixed high limit, but more than likely it would hit adjustable high limit first, in your case the first thing that goes off is the relief valve right?

Seasoned_Amateur

@GGross The sequence of events is this: Call for DHW, burner ignites, pressure builds in boiler loop over about 2-3 seconds, PRV blows. Is it possible that without the pump circulating, there's a lot more pressure created in the boiler? I'll post a current picture, too.

Seasoned_Amateur

Here's the set up as tested. I haven't piped the drains for my PRVs to the pipe with exposed solder on it in the back.

GGross

That would happen either way imo, without flow the boiler should shutdown on high limit, either fixed or adjustable before blowing the relief valve. the expansion tank on the discharge side of the boiler could cause pressure issues, though the pump isn't running so its not at play I suppose. The boiler should be able to run up to its fixed high limit without blowing on pressure, but the boiler does call for a slightly higher pressure than many other systems so it could be its all right at the edge. Generally a boiler blowing off on pressure after a couple seconds indicates an expansion tank issue, locking out on fixed high limit after a couple seconds implies a pump issue. Do you know if the boiler has a built in flow switch, or is it just a pressure sensor/low water cutoff?

GGross

did the boiler ever lock out on high limit?

hot_rod

On the loop take-offs you really need a purge valve on the return pipe before it connects into the closely spaced tees. It is about the only way to get a good purge on the secondary loops.

Seasoned_Amateur

@GGross Is there a way to test if an expansion tank has failed? There was no water coming out when I let air out of the fill valve. This tank is 15 years old. I could easily believe it's dead.

The boiler did not lock nor did it give error codes. I'm not sure if there's a flow switch on the boiler, but yes to LWCO. When I ran that DHW test, I think I was at 22-23# in the system. I've since lowered it to 20# which is what's spec'd. I've purged water through the boiler loop by closing the purge valve on the hot which routes water from my feed through the loop and through the boiler and out the purge. It flows very freely.

@hot_rod I purged the secondary loops through the purge valve on the outlet manifold. I guess I'm missing purging the section of pipe between the outlet manifold and my main loop. That photo doesn't show that I have a valve shutting off the exit on my outlet manifold and a purge on the other end of the manifold.

hot_rod

temperature rising quickly is usually caused by air locked boiler, air locked pump, or the boiler loop pump just isn’t spinning for some reason.

No power, locked rotor.

On some fire tube boilers I would hold the top relief valve open to blow out air that traps high.

I like purge and iso valves right in the loop where the tees are. This guarantees that you have purged the complete circuit. Assuming zone valves or actuators are all open.

hilltown

so what came about with the replacement pump?

Seasoned_Amateur

The replacement pump arrived yesterday. Took a few more days than promised for delivery. Installation was a real pain in the butt. The pump is front and center, but a fitting connects to the back of the pump with a retaining clip and proved to make a mockery out of me as I tried in vain to install it without being able to see what I was doing, nor get a hand fully back there—much less two—in order to press the fitting in and apply the clip. I had to disassemble several components to make it work and deploy a full list of profane terminology to get it done. Once in there, the pump fired right up when I set it into deaeration mode. Then, DHW worked great and finally, the radiant works perfectly. Total success! So relieved!

Big thanks to all of the folks on this thread who gave their time to offering advice and keeping me sane!

Merry Christmas!

Seasoned_Amateur

This Rinnai boiler is awesome, though I am a little shocked it arrived with a dead pump. The tech support said the units are tested and that the pump was working when it left them. Who knows.

The boiler puts out a lot more DHW than our old combi. Two showers at once with no pressure drop! Very satisfied now it's working.