I have a central boiler outside that heats my water with a side arm set up. It used to heat water great. Now, not so much. Amount of hot water is not anywhere close to what it once was. I have had it for 6 years. I have really hard water and flush the heater regularly to remove some of the hard water scale. Doesn't it have to be the mixing valve? What else could go wrong?
Wonder if the scale is building up on the inside of the pipe that runs through the hot water. Thus it constricts the amount of water going through making for less hot water returning to the tank. Either run new pipe which isn't a large amount or run a bottle brush through it backwards to clean it up?
Is your side arm as in a coil internally or a plate style heat ex changer ? Is the pressure reduction at all fixtures or just one? I have very hard water and when I flush my heat ex changer I also do shower heads and aerators.
It is not a pressure reduction, it flows fine. The temperature of the water cools off too quickly now. Used to have much more hot water.
It's possible you have an air bubble stuck at the top of your side arm, it will allow some flow but not full flow. I installed the pressure releaf valve at the highest point of my side arm. That way I can just crack the valve open for a split second, it bleeds the air off, and all works fine again.
I used to have a hot water front in a woodstove that would plug up from scale every 5 yrs or so. Couldn't ever "clean" it, had to make a new one each time. Have a pot of water on the woodstove now for a humidifier, probably has 1/2" of scale on it.
A Heating and Cooling co. can flush the coils with muriatic acid to clean the scale out. (fairly expensive)
Chet is right. Most likely the problem is accumulation of air at the top of the inlet. There is a small device that is on the high side of the piping on mine that is called an air eliminator. Works the same as what Chet has only is automatic.
moselgreenwing, were you able ta git it working?
I have the same problem with my setup that shows up every year - it's the buildup of minerals on the domestic side that does me in. I used a flat plate exchanger as my "sidearm" - as it's plumbed in parallel with the existing hot water tank, the potable water is constantly circulating through the exchanger. The 180 degree temperature the exchanger is being fed with will tend to precipitate out whatever minerals are in your potable water and deposits them in the exchanger; this eventually starts to restrict the flow that prevents the natural circulation from keeping the tank up to temperature.
I solved my issue by building a cheap de-scaling setup that I run at the end of every heating season to clean the exchanger. I have isolation valves and boiler drains with hose bibs above and below the inlet and outlets of the potable water side of the exchanger. I use a small submersible pump in a 5 gallon pail of non diluted CLR to constantly circulate through the exchanger for a few hours. This works like a champ and is safe just in case you don't get all of the CLR flushed out when you are done. Muraitic acid certainly will do the same job, but is far more critical to getting completely flushed out as it's really nasty. It can be rather risky stuff to use unless you're completely aware of what you are doing.
Is your sidearm heater hooked up to a storage tank (sidearm) to it, and to the boiler.
If this is the case, you wont see a restricted flow, because pressure is still going to tank, just not getting heated.
CLR cleaner works good, also the cheapest most acidic white vinegar works good too. When im cleaning coils, i start with the white vinegar, then move up. Cleaning too many times with the acid will eat through your heater.
You might check a plumbing wholesaler, or maybe homedepot has them, but i have a bucket with a pump and hoses that i use on tankless water heaters. You'll need to install valves on your sidearm heater to isolate from water heater, then 2 boiler drains, one on supply and return. Hook up hoses and fill bucket with vinegar and let pump run for an hour or more.
good luck