Trouble with Monitor MZ's flow switch

Unknown

Flow switch wouldn't make even though I had established flow with no presence of air and 15 PSIG in the system with a 1-2 PSI increase (?P) when circulator was switched on. The flow switch was in an open condition and just wouldn't close. When the flow switch was jumpered out - the unit would fire. I ended up adding water and increased the static fill pressure to 29 PSI and the flow switch is now making every single time. Strange thing is that now when switched on I see a pressure decrease of 1-2 PSI rather than an increase. This make any sense to you? I shouldn't need more than 15 PSI with all the radiant emitters below the unit. The flow switch should close with as little as 1-2 PSI fill pressure. Right?

They are back in hot water now but, I'm wondering just what was going on here?

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hr

Is it a flow, or pressure, switch?

I didn't realize there was a flow switch in the MZ, or did you ad one.

Pressure switches can plug very easily. Remove it and see if something is plugging the tiny hole.

hot rod

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Unknown

Flow Switch not Pressure Switch on MZ

Mounted near the bottom right hand side near the circulator. Part #9015 I think it's a paddle type?

Strange pressure situation. I don't use an auto fill valve on these units. I charge them up with a garden hose. In 8 month time I lost aproximately 13 PSI. Where did it go? Disolved oxygen?

Why the drop in pump differential pressure now?

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Ken_8

Sounds like...

Air in the system!

The pump head switched dynamics from positive to negative when you cranked up the static pressure. The trapped air probably left or became re-located and reverted to the pressure dynamic wherein you were pumping "from" a second PONPC (instead of the expansion tank PONPC) and the results were confirmed by the "flip"?

I am TSPing all new jobs of late and loving the results.

System contamination from the old systems is stuff a new Munchie would choke on. Ever seen that tiny s.s. HX? Awesome design - but not real good with buried "treasure" lurking in 30 years old piping and emitters.

I urge you to clean the water side with TSP, rinse and flush and fastfill once more. Betchu the flow switch will no longer be a "problem."



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Unknown

location of circ

Gary,

Circs on the supply out of the boiler or the return to the boiler?

skw

hr

I like to keep

an auto fill system on em for the first few months of heating. Even if it is a tempoary one with wash machine hoses fill and backflow valves.

Seems all radiant systems burp for a few months after firing.

Are you positive you don't have a leak?

Is the MZ pump acting as a primary pump also? Have you added to the small expansion tank capacity intergral to the MZ? Total system volumne? Make sure that funky little purger inside the MZ is not seeping. Mine did and it a weird metric size if you need to replace it

I'd stick with the Rhomar cleaners as opposed to TSP in this particular boiler due to hx material compatiability.

hot rod

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Brad White_2

Monitor MZ Experience

I agree with Hot Rod re: Rhomar versus TSP. TSP had its day and does a good job but if you fail to rinse thoroughly (it takes a LOT of water to make that slippery feeling go away) it can start its own corrosion cycle. I used the Rhomar HydroSolv on what was an old cast iron-on-monoflow system now hooked up in all copper to an MZ. I could not believe the stuff that was released by the Rhomar, this even after TSP some years ago. (I also dropped a ziplock bag of rare-earth magnets in a Neptune filter feeder to pick up the iron. Bag came out looking like a new black Chia Pet.)

The MZ I have pumps into the heat exchanger, drawing from the air purger, but at least the expansion tank connects to the pump suction side (PONPC). But that integral tank, the size of an Australian's bladder, is not large enough for my large-volume system. Pressure climbed from a cold static of 18 psig to over 30. So I use the MZ circulator as a primary and another as a secondary with its own Spirovent and Amtrol tank. Works fine it seems.

But what I did to the Monitor circulator by the way is this:
I replaced it with a Grundfos 15-58 with an integral check valve. This was to increase the flow rate to 6.5 GPM. Consider that the minimum flow of 3.52 gpm (800 lph) has a roughly 51 degree rise, you would need return water at 80F to stay below the condensing line. Now it runs about 28 degrees delta-T, so I set the aquastat at 130F and return water at design comes back at about 102F, all below the dewpoint.

Has anyone tried the new reset control? That is my next step.

Pressure loss: If not in the system, I would look at the connections to the back of the MZ. The threads that are cut have little taper and the gaskets are practically incompressible. My primary leak was at the pump suction where the fill connection is, but at the large nut that accesses the suction strainer screen. I replaced the black rubber gasket (which was crushed and rolled to a pulp) with flat red rubber which I had to make from sheet stock. So far no leaks.

BEW

Nick_12

Monitor

There indeed is a flow switch on the MZ, as well as two high limits, an aquastat high limit, and an air proving switch.

On the built in air separator, I've seen that screen get plugged up because the installer didn't do a proper system flush before start up.. you mighty want to check that.. its the large cap where the built in purge port is located right on the air sepparator.

The flow switch needs at least 3 gpm flow to switch too... if the boiler is piped in series with the heat emiiters, rather then primary/secondary, check to see if there isn't restrictions elswhere in the system... for example, I've seen 1/2" Pex used to supply a fin-tube baseboard zone... when more then one zone was calling, the flow switch would close, but when only one zone was calling (under 3 gpm with 1/2" PEX) there was not enough flow through the one zone alone to cause it to close. A quick fix would be to make use of the built in by-pass... opening it until the flow switch closes... check with the manufacturer drawings for location of this. I would only do this after knowing for sure this is the problem.

Have fun!

Unknown

MZ leaks & other observations

I've also had leaks at the pump suction side where the fill connection is behind the large nut that accesses the suction strainer screen. The black rubber gasket which seals the system fluid was crushed and malformed. It appears that these gaskets are not of the right size and thickness for this particular application. It also seems that they are being over tightened and compressed incorrectly at the factory. Once this connection is taken apart (to clean or check the screen) a new gasket MUST be used or made as Brad mentioned. Nearly impossible to find this gasket anywhere in a pinch.

I've had some trouble with the (NPT) threads on my last two MZ's as well. The threads taper on both were way out of Spec. Use LOTS of Teflon tape on those threads and plenty of elbow grease while tightening on your isolation ball valves or you’ll have a leak. TRUST ME.

Another thing I’ve noticed on the MZ is that when filling the system with their male garden hose connection, you always need to use TWO hose washers or your going to get wet. REALLY WET! Does this seems strange to you? Wondering if the French use different garden hose connections than we do?

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Weezbo

sounds vaugely ..like you are hitting a Pressure Lock.

seen a recirc aimed at the supply lines on the return of a boiler..that also no worky too good. Thanks for the observations it sounds like an adventure...maybe I hold off on recommending the MZ .....designe features are a Nusiance.

Unknown

Weezbo, Don't hold off

I still think that the MZ is an awesome product. Pete, Tom & Dieter @ Monitor are doing what they can to get these MINOR problems handled at Geminox's factory. I'd say their customer service has been nothing short of excelent and I still reccomend the MZ highly.

I power purged the entire system and heard/saw no air come out whatsoever. Will follow up in a few weeks and give it a dose of Rhomar now that I've lost the Bionball™ conditioner which comes with every MZ boiler. Still curious about the "flip" in pump differential?

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