Main boiler circulator cavitating when radiant loop is only open zone.

tink

Hello
I have a gas fired boiler supplying two taco valved zones serving cast iron radiators. At some point a pex radiant floor loop was added on to the system "plain vanilla" style - i.e. no mixing/temp reduction. This loop has its own circulator controlled by a thermostat. The system works fine with 1 exception. When the main zones (radiators) are not calling for heat (and the tacos are closed) and the kitchen floor radiant loop is calling for heat - the main boiler circulator still runs and it is noisy. I'm still trying to sleuth how this is wired up but it seems the boiler circ should not be running since there is no return supply to feed it. The radiant supply comes off the boiler right after the air scoop and returns to the boiler on the discharge side of the main circulator before it enters the boiler.
Any suggestions to zero in on fixing this? Appreciate any one's time and curiosity...
Tony

EBEBRATT-Ed

Sound like you don't need the boiler circulator to run for the radiant loop to work. Is this true?

I also recommend a mixing valve on the radiant. You will over heat your floors and damage the boiler from low water temp returning to the boiler. Radiant should not exceed 120 deg usually.

Without pictures it's hard to tell.

What I would do if you don't need the boiler circ to run for the radiant loop is ad a relay to shut the circulator off unless the Taco zone valves are open.

What starts the boiler up, the taco valve end switches via the thermostats or does the boiler maintain temp on an aqustat? Do you have a tankless hot water heater?

tink

Not sure if these pics are helpful. the bottom pic shows the radiant loop return just below the noisy circulator.
I agree on the radiant - although the system really has a very low delta t and I haven't seen the return water under 160F. the loops are not in contact with the floor...sort of hung in the joist bays. This system is only for heat - domestic hw is two gas fired tanks.

thanks for your input and help!

Zman

It would help to have picture taken from farther back or a rough sketch of the system. Where does the pipe between the air sep and the zone valves go?

tink

I will work up a sketch but the line coming off before the valves is the supply to the pex floor loop

tink

Jamie Hall

If your sketch is accurate -- and I have no reason to suppose it isn't -- it's perfectly obvious why that main pump -- which I presume is the one shown next the boiler, flowing downward -- is complaining. The wonder is that it hasn't destroyed itself yet.

Look at the diagram again: where, exactly, is it supposed to take water from? With both zone valves closed on the rest of the system, it has no flow at all. These things are partly water lubricated and cooled.

You don't show where the expansion tank is hooked in to the system. That would be helpful to know, too, but the way that thing is piped... the person who did it has a license?

tink

Exactly. funny thing is that its been doing this for 5 years since I bought the place! and who knows how long before that. good pump I guess....but I want to fix it and money is tight so I need to figure it out and diy the solution. The xpansion tank comes off the bottom of the air eliminator.

Jamie Hall

Is there a very good reason why you can't repipe it with a zone valve, instead of its own pump, and connect it in in exactly the same way the other two loops are connected? Not the best solution -- by a long shot -- but perhaps the cheapest.

tink

yes, maybe a good option. What if I just move the radiant return to "before" the circulator?

EBEBRATT-Ed

I don;t know.

To me this is an electrical issue not a piping problem. All you have to do is start and stop the circulator with the zone valve end switch. The only piping problem is the lack of a mix valve on the radiant loop.

@tink If you can make a wiring diagram and post it you can probably fix the issue with a relay, maybe 2 relays

Jamie Hall

That would work, too, @EBEBRATT-Ed

Zman

It looks like you could wire the boiler circ to the "COM" and "N/O" terminals on the zone controller and be done with it. The only issue would be if there is a minimum flow requirement on that boiler. Being cast iron, I kind of doubt it.

tink

thanks everyone.
@Zman - I'm going to explore wiring the circ like you suggest today...that makes sense but I feel I am missing something here...i.e., too easy? one thing I have to understand better on the valve controller is whether these 'dry contacts" are energized by the valve end switches or the thermostat call?

Zman

The zone controller is just a transformer and bunch of relays on convenient board. When a tstat closes, it sends power to the zone valve(s). Once the zone valve opens, it's end switch closes and the taco closes it's switch's to tell the boiler to fire and circs to turn on or off. If you apply constant power to the "com" terminal and wire the hot wire to the circ to the "N/O" termonal, the circ will turn on only when one of those 3 zones call for heat. The neutrals and grounds to the circ do not need to be switched, they just tie together.

tink

Ahh..I think I got it. i was thinking that Com was energized through the board...it is just made continuous with N/O but Com needs to be made Hot

tink

Unfortunately wiring circ through the dry contacts won't work because I still need to figure out how they have wired the radiant loop - just checked and the thermostat for the radiant is switching those contacts also.

hot_rod

An option would be to buy a 3 zone really box, ZVC. Wire the thermostats, zone valve and pumps.

The Caleffi ZVR103 relay box shown below allows you to run multiple pumps. So zone 1 has a dedicated pump relay, it could run by itself or when the other zones and pump run.

This example shows an indirect tank as zone 1.
In your case the radiant thermostat connects the zone 1, the radiant pump to pump 1, switch the two "status' to off. then other zones on 2&3 that pump on system pump.

HomerJSmith

I'm not thinking too well, today. I just breezed the comments.

My question is what turns on the radiant pump and how is it wired to the boiler aquastat? I see you have a zone controller (Taco?) with an added relay on it.

The relay in the aquastat is a two pole relay. One pole turns the boiler pump on and the other pole turns the low voltage gas valve on. What you need to do is to put a relay between the aquastat and the boiler pump which operates in a normally closed position and would power the boiler pump when the zone valves are calling for heat. When the radiant pump is calling for heat, only, the relay would open, cutting the power to the boiler pump and the gas valve would still get energized.

The TT connection on the aquastat would control the boiler operation. The zone controller connected to the TT would control the aquastat. The zone controller would also operate the separate added relay that turns off the boiler pump when only the radiant calls for heat.

Your current wiring dia would be helpful, but I could probably figure it out if I had the model # of the zone controller and boiler aquastat.

Some control of the temp going to the radiant circuit would more than likely be needed.

tink

@HomerJSmith - there is only one TT wire going from the Taco ZVC403 end switch to the Honeywell Aquastat relay L8148E. All thermostats go to the ZVC403 and all thermostat calls cause both circulators to run.

hot_rod

the relay box end switch calls the boiler. The boiler operating condition is controlled by the aquastat. That wiring should be internal to the boiler?

tink

@hot_rod - yes that is correct as I understand it.

HomerJSmith

One can easily shut off the boiler pump when the radiant pump is operating. However, that not solving the issue. The real problem is how to turn on the boiler pump when the taco valves need heat and the radiant is controlling the boiler pump's operation.

What about pump interaction when both pumps are working? You know, hydrolic separation. Maybe a Caleffi Hydrolink?

This may really be a piping issue that may be solved with a primary-secondary configuration. Or, it may be better if the boiler pump was on the supply from the boiler rather than the return to the boiler. The pressure loss thru the boiler is minimal.

How far is the radiant pump from the boiler? I think further analysis would require more pic of the sys and from further away.

tink

As I think about this more - why can't I just install a relay in the power to the boiler circulator that is switched by the taco valves? leaving everything else as is...so the existing controls still function as is, but the radiant zone can no longer start the circulator since I have a new switched relay in the main boiler power line?
@HomerJSmith - the radiant pump is about 12 ft from the boiler header.

HomerJSmith

tink, interesting idea. I assume you have Taco 570 z valves.

If the radiant pump is 12' away, how do you account for hydrolic separation when both pumps are operating? How are you maintaining proper flow thru the radiant loops? Do you have balancing valve(s)?

Your schematic diagram show the boiler pump pushing into the the return from the radiant manifold. There's a check valve there which is good. The problem is the pressure differential between the two pumps when both pumps are running. Both pumps are pushing against each other. I would think that the return from the manifold would go into the input of the boiler pump at least 12" from the boiler pump volute. Of course, the radiant pump would have to push thru the boiler pump volute for circulation thru the boiler to occur. Then you would have the problem of the boiler pump pulling flow thru the radiant zone when only the boiler pump is operating.

If you can shut off the boiler pump thru the zone valves that may work, but you still have 2 pumps pushing against each other when both pumps are running.

I see several issues aside from above:

Flow thru the radiant circuit.
Temperature regulation in the radiant circuit.
Return temp to a non-condensing boiler.

tink

@HomerJSmith ..correct

HomerJSmith

The problem with putting a relay (SPST normally open) connected to the 571ZV's, one thermostat would interact with the other. However, with two relays, one connected to each ZV, it would work. Then each thermostat with its own relay could when acting separately or together would control power to the boiler pump. The only drawback is that the transformer powering the thermostats must be able to power the relays too. The power to the thermostat is by the transformer in the Taco Zone controller. Is its current rating high enough for the loads?

You already have an added relay in the zone controller. What that relay does, I don't know. It may not be necessary, but it may opperate the radiant pump.

It is possible to gang transformers together to get more current, but it has to be done correctly.

One would connect the relay 24V leads from the relay to the #1 & #2 screws on the 571 ZV's. Bring a 110V supply to each normally open hi voltage lead of each relay and connect the other hi voltage lead from the relay to the pump. You would have to disconnect the circulator leads in the aquastat from the aquastat circuit board.

https://www.supplyhouse.com/Functional-Devices-RIBU1C-Enclosed-Pilot-Relay-10-Amp-SPDT-w-10-30-Vac-DC-120-Vac-Coil

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/RIBU1C-product.pdf

This is your best shot at disabling the boiler pump except when the ZV 571's are calling for heat with your present configuration.

HomerJSmith

I assume that the TT connections on the boiler are connected to the Taco Zone controller and not to the 571's directly.

If the Honeywell relay added to the Taco zone control is powering the radiant pump, then the use of the RIB relay would be a better replacement because the coil current draw is lower than the Honeywell coil. This would lower the overall current draw on the Taco Zone Control transformer.