Radiant Pump Failed - Do I need to Bleed System?

JoeDi · December 29

I have two radiant systems in my new house, this is the simpler of the two using a Viega Basic Heating Controller. I have diagnosed that the circulator pump is bad, the loop only works when the main circulation pump in the furnace room is running. This pump gets really warm when powered on and makes a ever so slight hum (and draws 120watts roughly) but it moves no water, you can hear nothing is moving.

I have found this pump on Amazon and am looking for guidance on replacing it. There are 2 valves on the supply and return so I can isolate this loop, but the radiant loops are all above it in elevation and i would imagine all the water is going to run out when I remove the pump. Unfortunately, I dont see any valves to shut off the manifold to prevent the water from leaking out.

Is there a way to prevent the water from leaking on these viega manifolds that I am missing? (the return side has the adjustment knobs but not on the supply manifold). Or do I just let it all drain and then let it refill? If so, I assume I need to bleed the air out of the system, can I do that myself without speciality equipment?

Thanks

Ironman · December 29

Just as you can turn the blue knobs on the manifold, you can also close the supply side by lifting the red rings and turning the flow setters clockwise.

By “lifting”, I mean moving them off of the flow setters. You may have to gently pry them away from the manifold with a screwdriver.

GroundUp · December 29

The pump appears to be in backwards (pumping downward?) so this might be a good opportunity to fix that as well. Lack of flow does not always mean a bad pump, it may simply be airlocked or that closed valve may be stopping flow as well. But to answer your question, yes a purge will likely be necessary after changing a circulator.

hot_rod · December 29

The valve to the right of the yellow handle ball valve, is that a check valve. It would have an arrow on it pointing up.

If so that valve and the yellow valve should prevent water from coming down from the boiler. Isolate all the loops as @ironman mentioned and you should be able to remove the pump.

Personally I would remove the 4 Allen bolts and remove the motor from the pump body. It could just have something stuck in the impeller. It may not need to be replaces, although I would have a new one on hand regardless.

A 4 mm or 5/32 T handle Allen wrench works best for removing those bolts.

If you buy the exact same circulator you can just swap the motors via those 4 bolts.

Screenshot 2025-12-29 at 12.42.51 PM.png

It's possible to do this without introducing much air. Install the new circ, leave the Allan bolts a bit loose. Then open the yellow valve slightly until water squirts from the pump. This may get any air out and the white air bleeders on the manifold may catch any remaining air.

Additionally the boiler should have an air purger?. Worth a try before doing a big purge and introducing fresh water and O2 into the system.

JoeDi · December 29

https://forum.heatinghelp.com/discussion/comment/1879718#Comment_1879718

My concern was losing the original balance of the system. Is there a way to mark them so I can get them back to where they were? I spoke with Viega when requesting a manual and they told me the blue knobs should be wide open and never used to control flow, which is interesting because mine are all at different positions, so I think someone who didnt know what they were doing tried to balance each room this way.

I have been able to remove the red rings, but the flow setters are no longer movable by hand.

Maybe it makes sense to start over from some sane base line anyways and just close these all 100% to change the pump and then re-open them 100% and then balance one at a time using a laser IR temp meter on the floor……

JoeDi · December 29

The valve is closed for the picture but I make sure its open when testing.

With that pump on there is no noise. On my other manifold system in the other room, you can clearly hear when water is pumping through. This system makes noise when the main circulator is on (and water flows through it) so I dont think the pump impeller is siezed up, as you can hear it spinning when its being forced by the main circulator pump in the utility room.

I would be surprised if its backwards, the other system has the pump facing the same way and its working fine. But I wouldnt rule out anything since a lot of people who had no clue have messed with this before I bought the house. The pump should be pumping UP towards the mixing valve, pulling hot water into the red supply manifold and then out through the blue return manifold and then back to the furnace, correct?

EDIT: The arrow on the pump points UP

JoeDi · December 29

https://forum.heatinghelp.com/discussion/comment/1879732#Comment_1879732

Yes i believe its a check valve, but the good news is that right above it out of frame, is a another ball valve anyways, so I can isolate everything in the picture with those 2 ball valves.

Removing the pump from the body sounds like a good idea, as long as its not likely to introduce a leak in that seal. I dont think anything is likely in the impellar because I can hear it spin when the main circulation pump is running and forcing water through it. Oddly though, the pump is consuming current (About an amp or so) and putting out an electric field so it seems like its doing SOMETHING, just not moving water.

Regarding the air purger for the furnace, do you mean to ensure there is no air causing an issue? I dont think that would be the case because the other manifold/pump is working fine (which can be seen here:) The difference between the two, this one uses an advanced heating controller instead of the basic heating controller, no idea why they elected to go with this over the basic, maybe its what the installer had laying around, idk.

hot_rod · December 29

Blue is the return manifold, so the pump is correct pumping up towards the mix device. If it has worked fine for years, it is ok.

The correct way to adjust flow is to first know what each loop was designed for, but...

Those plastic indicators also turn to make flow adjustments, that is usually where the adjustment is made, the blue valves should be wide open. So no problem turning the blue valves closed all the way.

On the red valves, pop the red ring off. Usually it is a hex shape, so it is the wrench to turn off or adjust flow. Slide it down on the clear plastic indicator and turn .

Count the turns it takes to close the valve and write it down for each loop, CW clockwise to close.

JoeDi · December 29

https://forum.heatinghelp.com/discussion/comment/1879758#Comment_1879758

I was planning on opening one at a time when this is done and using my thermal camera to figure out exactly what each loop does. Then I will be able to adjust things down the road if needed.

Someone def thought they could balance the system using the blue knobs because they are all at various open positions…

My concern is I have never bled a system before and this one is pretty damn complicated. Even if I shut off the 2 ball valves and close each loop, and I let water flow out before tightening the allens, I am still going to introduce SOME air to the system, correct?

Red arrow points to bleeder for whole system, correct?

There is kind of a lot going on. Besides the indirect and the DWH recirc system, there heat feeds multiple heat exchange packs that sit on the forced air systems for each zone.

JoeDi · December 29

this shows all the circ pumps in the utility room

Ironman · December 29

I think that you’re more concerned with balancing than you need to be.

Once any air bleeding that’s required is done, just leave all the flow setters wide open and see how the system works for a few days. If all of the loops are close to the same length, you shouldn’t need any adjustments.

To bleed air:

increase the system pressure at the fill valve to 25 psi
Open the yellow supply valve above the pump
Connect a drain hose to the drain connection at the end of the return manifold
Turn off every flow setter and blue knob on the manifold
Bleed air by opening only one flow setter and its return knob at a time. Do this with the drain open
Close the loop and repeat the same on each loop, one at a time.
Return the fill setting to 15 psi and let out pressure at the drain until it returns to 15 psi cold.
Open all valves and flow setters.

hot_rod · December 29

In reality there is not a lot of difference between the valve mechanism in the red or blue side. They both use flat EPDM washers. Flow could be regulated with the blue valve. Doing it on the flow indicators just simplifies the setting as you turn the knob. I suspect you indicators are fairly fogged and may not be easy to read anymore?

When the blue cap is removed and a thermal actuator is installed it basically acts as an on off valve that slowly, over 3 minutes or so opens, so it does operate at partial open conditions often.

No harm in trying to make the repair or sway and re-pressuring and see if it circulates. Small air will make it's way back to the purger above the boiler at some point.

Worse case you do a loop by loop purge.

I don't like seeing indications of that flue running in condensing mode, the water streaks on it. That could indicate long cold run cycles on the boiler.

A boiler like that connected to radiant really should have some return temperature protection. A look inside by the burners or a mirror in the flue damper would indicate it's health.

Might be a good idea to get the covers back on those breaker panels!

Ironman · December 29

Good catch, Bob. I didn’t see the water streaks until you mentioned it and I zoomed in. It also looks like it connects to a larger chimney which would add to the problem.

hot_rod · December 29

https://forum.heatinghelp.com/discussion/comment/1879794#Comment_1879794

@EBEBRATT-Ed always catches the electrical atrocities. Hopefully he is enjoying a day off :)

JoeDi · 5:16AM

https://forum.heatinghelp.com/discussion/comment/1879791#Comment_1879791

Yeah they are pretty hard to view…. Under the blue knobs are just plastic valves, they are different than yours.

Regarding air making it back to the purger above the boiler, how will i know, or it purges automatically?

what kind of return protection should it have? One tech I had come out thought I should replace the mixing valves with buffer tanks, but his reasoning had nothing to do with cold boiler run protection.

I havent looked in the oil boiler myself, but I had a company service it when I moved in and they didnt comment on this or the health at all.

(yeah sorry about the panels, I am replacing a lot of switches with zwave switches and its much easier to use the circuit breaker finder probe tool with the covers off :)

hot_rod · 4:08PM

Usually you rotate those plastic indicators to adjust flow. However based on the age and knowing plastic gets brittle after time, you might not want to wrench on those plastic components.

It should look similar to this under the blue knob. As you turn the blue cap it pushes or releases this pin to move the valve mechanism.

Did Viega tell you how to make flow adjustments when you talked with them? Maybe send them a pic of the manifold to identify the vintage and parts available.

How much change or upgrade do you want to attempt? Perhaps Viega has rebuild parts for the manifold if you want to use and view those flow meters. Adding a boiler protection valve would take some work and drain down.

If you hear the pump spinning or vibrating, pulling current, not getting excessively hot, you could just have some air locked loops, or the mix valve jammed in a cold position?

Might be better to wait out the heating season to make major changes or upgrades.

I'd be saving for a mod con boiler upgrade based on the radiant system and a boiler that age and being potentially oversized?

Radiant Pump Failed - Do I need to Bleed System?

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