If you are interested, Naphtul, on a warm day perhaps re-pipe as shown in the quick pencil sketch below. I apologize that I'm not the best drawer of things. Not shown are the down-stream zone valves, if any, and the radiation. They go after the pump. The return piping isn't shown.
Your zone valves can be on the supply or return. If zone pumps, instead of valves, are used, they go on supply, with flow control valves.
With this set up, often called "Pumping Away", your pressure will be perfect and purging air is easy and quick. You won't have to ever use the on-radiation bleeder valves (coin vent, Maid O Mist, etc.) Your system will be silent.
As Arctic Bill said, it is very important that the relief valve be installed on the boiler. Some boilers, however, don't have an extra port for the relief valve. If that's your situation, install the relief valve on the return side as close to the boiler as possible and with absolutely no valves between it and the boiler- Pretty much like you piped yours.
(Supply side is OK, but on return the water is a little cooler, thus the diaphragm in the valve might last longer.) Test this valve at least yearly. I also think I see a low water cut off device. Excellent!
CAUTION! Boring Stuff Ahead!
You mentioned corrosion and clogged pipes.
There should be none unless air is somehow getting in or the water is replaced often.
An idea for you is sodium molybdate treatment after fixing any reasons new water is entering. Not only is sodium molybdate an oxygen scavenger, in the presence of oxygen it will create and deposit a protective oxide coating on the ferrous parts of the system.
At high concentrations, it's a very effective cleaner, scrubbing off the gunk on the pipes and suspending the sludge in the water. While cleaning it will start to form a protective coating, filling in any rust pitting inside the piping & other ferrous components.
For the initial clean-up, flush the cold system, paying special attention to the boiler where sludge collects. Then install a wye-strainer on the boiler piping return side. Add sodium molybdate to about 300 mg/L. Higher is OK, but not beneficial, cost wise.
Let the system circulate several days. You can do it with the heat off if this job is a summer time project. After some days, clean the strainer's screen and flush the system again. Run it a few more days if the screen had debris. Clean the screen one more time.
Now, install the sodiuym molybdate to about 100 - 150 mg/L. Any time new water is added, re-test the concentration or measure water removed to know how much chemical to add back.
How It Works-
Sodium molybdate is an oxygen scavenger, holding the molecules in suspension until they react with ferrous ions. It forms a ferrous molydbate complex which oxidizes and deposits a ferric molybdate complex combined with ferric oxide. It's insoluable, thus the protective deposits. This coating is passive until oxygen tries to get to the iron in the piping, pump and expansion tank- boiler, too. You will see it as a brown powdery substance inside the pipes next time you open the system. It'll be inside the copper, too but doesn't cause problems soldering.
Results-
I've worked on industrial systems that have constant new water added (and new molybdate added automatically to maintain 100-150 mg/L) Pumps didn't cavitate, welds on piping didn't rust, threaded joints came apart easily with no breaking. The spray from the cooling towers' mist cleaned off the exchangers quite easily, too. Even the dreaded copper-to-steel pipe connections showed no galvanic corrosion.
I maintain 125 mg/L at home and my early 1950's boiler has no rust or sludge on the bottom. The 1920's steel piping comes apart easily for modifications. I have not lost a pump nor an expansion tank since I started doing this. (I also have a Spirovent instead of an air scoop.)
BTU decrease is negligible, as demonstrated in lab testing. The coating is an excellent conductor of heat.
It may be worth the time and cost to protect your system. Shop around for cost, as some places have fancied up versions with other stuff added.
I hope this helps you get your system optimized for low cost operation and longevity.
Paul
PS: Your pipe work looks very nice in the photos. Very professional joints!
