My advice would be to get this junk removed ASAP before something bursts and you have a disaster on your hands. Get rid of it completely, or if you want to get it fixed up, get a new pump (Grundfos makes great pumps, but I can't imagine that this pump is usable at this point) and tell the plumber to connect the recirculating pump to the T&P relief valve inlet, which is not currently being used(?), rather than the drain. Doing this would reduce the scale/sediment buildup greatly, which happens mostly near the bottom of the tank. Replace all of the pipe in the vicinity of the pump as well, as it is probably completely scaled up and corroded. Everything else should be ok.

My perfect advice would be to return the feed immediately back to the top of the tank on the cold side, check valve included. This way continuous circulation happens inside the tank rather than taking chances with a whole house system. You might also install an extra pump at the top of the loop to help balance out the bottom pump, etc. A third pump in between is optional although highly recommended. The idea here is to get the water spinning fast enough to cause friction ergo the generation of heat.

Actually the return loop line coming back to the tank should have the pump at that point. After the pump the return line should run back to the cold supply line to the top of the take with a tee and shut off valve on both legs of the tee. One leg should go to the cold supply in with a check valve on the cold supply side to prevent the hot water from backflowing into the cold supply. The other side of the tee should go to the hot supply line to feed the house with a check valve to prevent backflow. the shut off valves on each leg should be close 1/2 to divert roughly equal flow to the tank and the hot supply. This configuration will give you true circulation of the hot loop as intended.

In pilot-operated pressure reducing valves, a pilot valve is used to load a piston or diaphragm that increases the downward force used to open a larger main valve. This enables larger flow capacity with a lower pressure offset (droop). The opening and closing of the pilot valve is controlled by the balance of force between the adjustment spring and the secondary pressure in the same manner that a direct-acting valve operates. However, in a pilot-operated PRV, this opening and closing of the pilot valve purposely delivers pressure to the main valve piston or diaphragm. This pilot flow pressure then causes a downward force that is amplified by the area of the piston or diaphragm to enable opening of a much larger main valve, which in turn provides the ability for very high flow rates.

This device recirculates the water in those hot water lines by placing a sensor and a valve at the farthest end of your hot water line that senses when the water in the hot water line has dropped below 95° F, opens the valve and “trickles” the water out of the hot water line into the cold water line until the water in the hot water pipes gets back up to 95° F or so.

Fig. 2 Delivered steam pressure is regulated by balancing forces acting directly on the valve itself: the downward force caused by compression of the adjustment spring against the upward force from the secondary pressure acting against the underside of a bellows or diaphragm.

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check valve is looking a little crusty. they dont hold up well in potable water. cold water from the bottom of the tank will "back" through the pump amd mix with the hot giving you the diminished hot water that you descriped.

In pressure reducing valves, the mechanism that automatically adjusts the downstream pressure typically uses the balance of forces between the steam pressure and an adjustment spring. At present, this is a universal concept on almost all manufactured pressure reducing valves. However, there are two different ways in which this mechanism is implemented to control the amount of valve opening:

From the above characteristics, it can be seen that the function and applications of non-piloted direct acting PRVs differ substantially from those of pilot-operated PRVs.

Very interesting problem you have here. Both Mitch and Michael are right and cover the potential problems. I'm gonna add a third observation. I personally would NEVER allow heated water to infiltrate the cold water supply. The water coming from most water heaters is filthy, dirty and full of bacteria.(especially if temp is set below 140F) The sediment in the bottom of most heaters is nasty! I always advise my customers to never use hot water for potable purposes unless it is going to be boiled in the process. With that said, the closed systems I have had installed cycle the unused hot water back into the cold water supply to the heater tank with a back flow preventer installed in the cold feed to prevent the warm water from entering the cold supply by siphoning. The system as pictured looks to me like a quasi sediment agitating system, by pumping water in from the bottom of the tank. NASTY!!!! There is a reason for a drain at the bottom; to get rid of sediment as well as drain the tank to replace it. I would rethink this system, get some advice from a Master Plumber that knows how to install a recycling system if you feel you need it. Most residential users do not need instant hot water, have the high volume usage or have hot water outlets located so far from the heater to justify the additional operating costs of this type of system. Don't get me wrong, loop systems are great if the lines are well insulated, and the volume of hot water required can justify the cost.

Because the downward force is amplified through the use of a piston or diaphragm, a small change in the opening on the pilot valve can result in a large change in flow and downstream pressure through the main valve. As a result, there is little change needed in adjustment spring force on the pilot to accomplish quick response over a wide range of steam flow rates. Quick response and tight delivered pressure control represent the main advantages of this type of valve over the direct-acting type.

In a steam-using plant, steam is often generated at high pressures and reduced locally to provide heat for each steam user. This is usually done to minimize the diameter of steam distribution piping and enable more cost-efficient steam delivery.

I see a line (the CPVC that goes into the wall) for what I hope to be a T&P valve, but I can't see where the actual T&P valve is. If it's tee'd off of the hot water outlet, then that's fine. I'd hope it's not simply laying on top, not connected to anything, but I don't have enough faith in whoever installed this to take that for granted.

Fig. 3 Delivered steam pressure is regulated in a similar manner as direct acting PRVs, however indirectly via a pilot valve. As the pilot valve is actuated, it provides the opening flow to the larger main valve which can supply significantly higher flow rates than the pilot itself. The pilot valve is then equalized by the secondary pressure, which correspondingly controls the opening flow to the main valve.

A common way of lowering pressure is by throttling down the size of the steam passageway. For the most basic pressure reduction, it is possible to simply use a conventional globe valve in a fixed partly-open position, or by inserting an orifice plate into the flow of steam. However, any fluctuation in flow rate would be accompanied by a corresponding fluctuation in pressure. To avoid such circumstances, pressure reducing valves (PRVs) can be used to provide precise control of downstream pressure. They automatically adjust the amount of valve opening to allow the pressure to remain unchanged even when the flow rate fluctuates.

Calculate and display steam property values using pressure-based saturated steam tables, temperature-based saturated steam tables, and heating steam tables.

In direct acting pressure reducing valves, the amount of valve opening is determined directly by the movement of the adjustment spring. If the spring is compressed, it creates an opening force on the valve which increases flow. As pressure builds downstream, equalizing occurs by feeding the downstream pressure to the underside of the adjustment spring (usually against a bellows or diaphragm) where its upward force counter-balances against the spring compression. Spring compressive force which opens the valve is limited to allow sufficient spring sensitivity to equalize with downstream pressure changes. The net result is simple pressure control through a valve orifice where high flow rates can cause pressure droop.

Moved into a house recently that was built in 2006. There is a hot water recirculating pump installed (Grundfos UP 15-10 pump). I'm not very knowledgeable about plumbing from a DIY perspective, so I could use some help here.

What the manual is describing is a system without a dedicated return line. The valve at the furthest point allows previously hot water that is now cool to go into the cold water pipes backwards and the pump pushes hot water back into the hot pipes up to that valve. With an existing install, this is probably the easiest way to do it, but I prefer an install with a dedicated return to avoid getting the water from the hot water tank in the cold lines (not a fan of the mineral taste). It looks like you have the latter setup.

I'm having some problems with it now, as it's no longer providing hot water as quickly as it used to. I looked up the service manual for it, and it calls for an installation different than what I'm actually seeing (not sure if this is the problem, but I want to understand). The manual specifies:

First off, it's quite possible that the segment of pipe between the pump and the "tee" attached to the drain valve is completely or partially clogged with (corrosive) scale/sediment buildup. Judging by the scale buildup on the outside of the pipe just below the tee, it looks like the tee is leaking (why? corrosion?). I can only imagine that the inside is worse. Even the check valve and the ball valve upstream from the pump look like crap. In fact, I'm pretty sure that's calcium on the ground below the check valve (thing between the pump and the drain with a hex bolt -shaped top on it), indicating that it too is already leaking. The check valve almost certainly isn't functioning properly (check valves are intended to only allow water to flow one way,) which is possibly why you are having to constantly readjust the temperature in your shower. The cold water gets injected into the tank at the bottom (via a long "dip tube" that enters at the top and travels down to the bottom.) If this check valve is being held open by sediment, or if it has failed due to corrosion, then cold water could be coming out of the water heater from the drain at the bottom, making your "hot" water turn merely "warm" after about 10-15 gallons of use, which is one possible explanation for your "shower get[ting] colder during use" problem.

While it is possible to maintain a constant pressure by using the combination of an actuated control valve, a pressure sensor, and a controller, a pressure reducing valve offers the advantage of being able to control pressure through fully-automatic self-contained operation, requiring no type of external power source. It can offer the further advantage of extremely rapid response action by immediately sensing and adjusting based on the downstream pressure.

You're sorta kinda in a bit of trouble here. This system is close to being good, but because of a seemingly minor screw-up, you're going to have major problems here. The recirculating pump SHOULD NOT be connected to the drain.

The first thing I'd check if you're having problems is when the timer is set. You typically want this to run shortly before you get up in the morning to use the sink/shower. Over time, with a power outage now and then, it may be running after you need the hot water.