Hammering on zone turn-on

adk0212

I'm working on solving a water hammer problem in a 2-zone hydronic heating system. The system consists of a Prestige Solo 110 boiler which powers two CH zones plus a DHW indirect tank. The boiler has an internal circulator pump which is plumbed in a local loop per manufacturer's recommendation. The CH loop has a dedicated Grundfoss UPS-15-58-FC  circulator feeding 2 Taco Z075C2-1 zone valves. The DHW loop is fed from a dedicated fitting on the boiler and has its own Grundfoss circulator (no zone valve). A B&G HFT-30 expansion tank and Spiro-Vent Jr. are installed on the system return.



The water hammer is triggered when either zone valve OPENS independently. (If a zone is already open, the second zone opening will not hammer.) There is no hammering when any zone closes, only when opening. First there is a "rushing" sound that lasts 1-2 seconds followed by a hammer. I can hear water "trickling" through the zone for about a minute afterward.



I can trigger the hammer by manually opening a zone valve when no pumps are running. To me this says there is some sort of pressure differential building up or maybe an air pocket?



I've tried bleeding the zones multiple times and never manage to flush any significant amount of air out. I keep the end of the drain hose submerged in a bucket of water and see no air bubbles coming out. After bleeding the system will usually run quiet for few cycles before it starts hammering again.



I've turned down the speed on all three circulators to low and it doesn't make any difference.



All components are brand new.



Any ideas on what I should try next?? Thanks in advance!

icesailor

Check This:

It sounds like a check valve installed in a location where it is isolating a space in the piping between the zone valve and a check valve. There is high pressure in this area and it is released as the zone valve starts to open.

If you have internal flow checks in the circulators, try removing them and see what happens after that. You don't need the checks if you use zone valves. They are really just motorized check valves.

IFC's, another idea gone really bad on occasion.

IMO.

Try draining the water out of a house for the winter and not know that they are there. When you come back in the Spring, you may have a serious insurance claim on your part and some serious explaining to do.

adk0212

Great idea

That's a heck of a good idea! The CH pump has an internal check and the pump is in a vertical orientation directly below the zone valves. Gravity could definitely create pressure zone there. I always wondered why that IC was needed given that I have zone valves. The installer was in such a hurry since he was already a day over on the project he probably never bothered to remove it. I will remove it tonight and report back.

adk0212

Nailed it!

icesailor, you're a genius! I removed the internal check from the CH circulator last night and the hammering is gone! First uninterrupted night of sleep since the heating season began....

adk0212

Spoke too soon

Well I spoke too soon. It's been unseasonably warm lately so the boiler hasn't been running as much as usual. The hammer is still present. It sounds a little different now, but it's still doing it. Previously the hammering included a ricochet like noise, which I now suspect was the water bouncing off the check valve. That part of the noise is gone, but the initial hammer is still loud and clear.



The noise appears to be louder the longer it's been since the boiler ran. The first cycle in the morning is especially loud after it's been idle all night.



Any other ideas??

NRT_Rob

do your zone valves have end switches?

if so, wire them so that the end switch turns on the pump. sounds like your pump is cranking up before the valves can open. this is bad for the pump, and your valves.



the other possibility that we've... ahem... run into once or twice... cough... is an undersized or malfunctioning expansion tank. hard to think that a 2 zone system would be too much... but then, a solo 110 is pretty big for 2 zones, how big are these zones?

adk0212

Yes...

The zone valves do have end switches and the pump is wired to them. I've verified that no pump runs until the valve is fully open. What's especially interesting is that I can reproduce the hammer with all power to the system shut off, just by manually opening a zone valve.



How would you recommend testing the expansion tank? The expansion tank, spirovent, and city water supply are all plumbed into one fitting in the return side of the system.



I have compared pressure in the primary loop (via the built-in gauge on the Solo) and the secondary return (by screwing a simple water pressure gauge onto a drain cock and opening the drain). The Solo reads ~15 psi pretty consistently. The return side is reading ~20-22 psi, but so far I've chalked the difference up to my rinky-dink pressure gauge not being very accurate.



The Solo 110 is likely oversized for this house. It's supporting 2 CH zones and DHW. Each zone heats ~1000 sq ft via ~90 ft of finned copper  tube baseboard.

NRT_Rob

hmm

that is interesting.



first, tap on the xpansion tank and if it sounds like a thud, it's not working. but I have to admit the no power hammer does have me puzzled. it would almost have to be a bad zone valve... can you make either one hammer, or only one?

adk0212

Both

Both zones will hammer; whichever one opens first. If the second zone opens while the other is already open, there is no hammer. The first zone to open seems to relieve the pressure.



The top third of the expansion tank sounds solid, the bottom 2/3 sounds hollow.



Do you think there could be an interaction with the DHW loop? The DHW pump still has its check valve installed since there is no zone valve on that loop.

kcopp

What is the system...

running @ for pressure? I would say try a Delta P circ but if you can make the system hammer w/ nothing on..... No other check valves in the loops, other than the ZV?

adk0212

I thought...

there are no other check valves...BUT after looking at the piping for 100th time I noticed a fitting in the return line I'd never seen before...and I think it's a check valve! Markings says "Watts" and "250W00" I think...hard to read. There is a device on Watts' web site that looks identical..."Bronze Maxi-Flo Check Valve" It has a direction of flow arrow so I'm thinking this must be a check valve.



So! After claiming all check valves were gone, apparently I'm mistaken! Good news. I will see about removing this device...I don't see why it would be necessary given that both zones have ZVs. I will have to see if my copper sweating skills are up to the task of 1" tube...

adk0212

It's gone

It was definitely a check valve...and now its out of the system and in my bin of misc plumbing parts. Soldering the 1" copper wasn't too bad, but I did resort to using Mapp gas on one fitting instead of just propane. It's too soon to tell if removing the cv has fixed the hammer, but I'm cautiously optimistic. I can imagine that as the water in the zone cooled after a cycle, the cv would close and the shrinking water would cause a vacuum in the zone lines as compared to the primary loop pressure. Fingers crossed.

Gordan

The reason for checks...

Although the zone valve on one end (whether supply or return) will stop flow from that end, it will not stop so-called ghost flow (caused by buoyancy) on the other end. Unless there's a heat trap, which would be in the form of piping taking a downturn for 18" or more, you could have, for instance, DHW return in the warm season making its way up to your baseboards and causing ruckus. The larger the pipe diameter and the bigger the heat differential between the cool water at the top and the hot water at the bottom, the higher the likelihood that this might happen.



See, if you had your zone valves on the returns of the zones, and the check on the supply (put it back in the circulator), then this would/should not happen because the check allows for pressure equalization into the zone (it lets water pass from the constant pressure part into the part where pressure drops as water cools.)

adk0212

Point well taken

Nicely put, Gordan. If only my expensive "professional installer" had known these things! As it is the only skill he seemed to have was the ability to solder copper pipe, and even then he completely ignored the need to support the pipe securely. At one point he called TT tech support to figure out how to program the DHW settings and after the tech walked him thru it step by step he said "Glad I called, I would never have figured that out!" to which the audibly frustrated phone tech replied "You would have if you read the manual."



Moving the zone valves would require more re-plumbing than I'm ready to take on at the moment. I'm proud of myself just for removing the check valve and soldering in a bypass cleanly! If migration does turn out to be an issue there is an isolation valve I can throw to cut off the CH returns. Of course it will be rather important to remember to open that up again before the next heating season.

adk0212

Fixed

Really this time. System is dead silent at zone turn on now. Many thanks to everyone who helped solve it!