why bubbles when only kitchen zone is active? A theory. Kristi's most peculiar symptom is that the problem only occurs when the kitchen zone is working by itself. I have an idea of why that might be, and this could explain lots of troubling air bubble problems. This has to do with the pressure drop caused by the circulation pump. The pump's job is to generate pressure between its inlet where it is low and the outlet where it is high. The amount of pressure change depends on the resistance of the pipe system. When only one zone is open this resistance is high and the pressure drop is large. The pressure right at the inlet to the pump can then be very low if the pump is powerful and the pipes to the zone are small. If this pressure gets really low, bubbles of water vapor can form. The way to check for this problem would be to put a pressure gauge on the drain outlet on the return side of the system just ahead of the circulation pump. If this pressure is negative, the solution is to reduce the pressure drop by reducing the power of the pump. Any thoughts, Baymee?

Kristi, While there are a list of items which should be corrected on your boiler system, the main one is air in the system. The Gurggling or running water sound is the air trapped in the system. If your toe kick heater was installed properly, there should be an access panel in the bottom of the cabinet where it was installed. Also there should have been a air relief vent installed at the high point in the hot water piping. The air vent can be several different types opened either by a screw driver, coin or special square head key. If there is no air vent you can also eliminate air by making sure there is adequate air pressure in the system (typically 30 psi) at the boiler. Then you have to increase the velocity of the water thru the piping where you want to eliminate the air. This maybe a problem with your system due to the piping arrangement. Pump cavitation is usually a swishing sound which is loudest at the pump. Your system was originally installed with a primary (Black) pumping system which is normally sized for the boiler capacity, meaning you should not need additional pumps. The Grundfos (Red) pump is considered a secondary pump, which was installed incorrectly. It appears the secondary pump is pulling supply heating water from the top of the boiler and also past the Temperature & Pressure relief valve (T&P valve). This arrangement guarantees that air will be supplied to the toe kick heater via the relief valve opening and cold water makeup. I would try eliminating the secondary pump and piping down to the relief valve and plug the tee at the relief, then tap into the hot water supply line creating a new zone. You would also have to install balancing valves for the existing zone and new zone. By doing this you can now force water through the toe kick heater utilizing the primary pump. I would also add an air vent to the toe kick heater. Additional things to consider correcting. In a boiler system there is a theoretical point of zero pressure. This point should be located just prior to the suction side of the pump. The suction side is a low pressure area where you should locate the "System" air eliminator (Air scoop) and expansion tank. This is also where you should be providing makeup water to the system. You should provide a tee in the bottom of the air eliminator and this is where the expansion tank and cold water makeup is teed in. You have an automatic makeup water valve which should be adjusted to always keep 30 psi in the system. Maintaining water pressure is the only way to keep air out of the system. Always bleed the air from the radiators too. Your auto air vent on the top of the air scoop looks crooked and may be hanging up too, may have to be replaced. There is a small schrader valve on top of the auto vent, try closing and opening and listen for air to come out, then make sure it is adjust slightly open to automatically bleed system air. The T&P valve relief pipe should be piped to within 6" of the floor to avoid splashing of extreamly hot water. If the relief pipe is cut at a 45 degree angle the water will flow out of the pipe more straight (Trade secret). You have a ball valve installed at the expanion tank - on the expansion pipe. This is very dangerous because if this valve where inadvertantly closed the only additional safety you have on the system is the T&P valve. If the T&P valve malfuctions too or is replace with an incorrect rating, the system can explode. If you leave this valve in place please put a tag on it stating "This valve is to remain open during system operation". Otherwise remove it, contractors put these here so when the expansion tank gives out (Leaks) you don't get sprayed while changing out the tank. Hope this all helps. Dan Martyn

Yeah, we have one and it just holds the shallow roasting pans that used to be under the broiler in our old range (now we have two ovens, so no drawer there). It's barely worth including, let alone rearranging important stuff for!

They could have inserted a vent elbow similar to this one to get the air flow turned 90 degrees. https://www.homedepot.com/p/3-1-4-in-x-10-in-Short-Way-90-Degree-Rectangular-Elbow-90E3-25X10/100138324  Then extend it with standard 3 1/4"x10" ducting out to the toe kick, and install a grill. I would hesitate to completely remove the cabinet itself just to punish the contractor with reworking a bad job. It will disturb the countertop, backsplash and other things that are already installed to your satisfaction. I have a hydronic toe-kick heater, and we cut out a large square area in the bottom of the sink cabinet, using a jig saw. We then screwed small metal support plates under each corner of the opening so that the cut out section rests on the plates when you put it back in. It is not readily visible when you drop the cutout section back in, and in my case it gives me access to both the pex hydronic lines and the motor for the booster fan that is part of the heater. Bruce