Does this make sense?

Ken C.

Yesterday afternoon, I replaced an ignitor, flow switch and hy-vent on a customer's boiler (a Laars EBP-110). I only drained a little bit of water from the system to relieve the pressure so I could change the hy-vent. After replacing those parts, I didn't purge the system (single zone) because the return was coming back nice and hot.

Today, the customer called me back because her baseboard made a loud banging sound when she used the hot water. On the Laars EBP series, anytime domestic hot water is running, a zone valve inside the boiler will close, preventing circulation in the heating loop. Each time that valve closed, the pipes shook and banged once (sounded just like water hammer). The boiler room piping was very poorly supported and was hitting the framing and foundation in some spots, so I added hangers and insulators, but that didn't help.

I also thought the zone valve (motor actuated, with a spring return) might be closing too quickly, so I timed it and compared it with another unit, but the valve was closing normally.

I called Laars tech support, who recommended putting a bypass between the heating supply and return, but I didn't see how that would solve the problem.

Next, I checked the boiler pressure and saw it was high (25 psi), the other two units were around 10-15 psi. When I reduced the pressure, the banging went away. I told the customer to keep an eye on the pressure gage, and that if it goes high again, the PRV will need to be replaced.

I've never heard of 25 psi of boiler pressure causing water hammer before. Is this something peculiar to Laars EBP boilers?

What about Laars tech support's suggestion about a bypass (which they described as teeing into the supply and return risers and a piece of pipe between the two)? I don't understand how that would correct a water hammer problem.

Alan_6

water hammer

I had a situation simular to this with a Bryant boiler. It has a three way honeywell zone valve,for the domestic water tank. The end switch makes and turns on the pump before it is fully seated, and was causing a hammer. I installed a delay on make relay to the end switch, set it for ten seconds, to allow the valve to fully seat before the pump came on. Is there a valve on either side of the pump, where you can slow down the flow? This would help prove if you need a bypass.

Paul B._2

Endurance EBP

Hi Ken,

The Endurance has an internal circulator and is similar in design to the old Heatmaker HW models. There are a couple of slight differances however.

On a Heatmaker you always needed an external circulator to move water out of the boiler, and into the system piping. The external circulator, and the internal circulator were de-coupled by the storage tank, and couldn't see each other in series.

The Endurance internal circulator is designed to provide adequate flow through the boiler, and some external zones. When you need an additional circulator for your zones the prefered method of piping is Primary/Secondary. This helps de-couple the system pump fron the boiler pump in larger systems.

I regularly see systems where we have the system pump and the boiler pump in series, and as long as you use the Blue wire to control the system circulator, and drop it out on a call for Domestic water it really isn't a problem very often. As you can imagine, when you have two circ's in series the water velocity can get pretty high, and when that priority valve closes all that water comes to a screetching halt - bang.

My guess is that with the proper system pressure - 12psi most expansion tanks take up the "bump" when both pumps are in series. With 25psi in the system your expansion tank was effectivly reduced in size and capacity, and so the customer started hearing the water hammer, only in domestic mode. As the priority valve closed aganst the flow from the external circulator the velocity of the water in the piping caused a water hammer, even though the Blue wire may actually shut the circulator down as it should.

With the correct fill pressure, and the correct air charge in the expansion tank, this may not act up again. If it does, the method of piping Tech support suggested will make the boiler Primary/Secondary, and eliminate the issue.

Sincerely,

Paul Bock

Applications Engineer, Laars Heating Systems