Every day is a learning experience in this business. We all hope that we learn things as "cheaply" as possible, but reality is over the years there are the jobs that you loose money on while learning lessons. The measurement is: How much did I pay to attend that class? With that said.
Decide if you're going to stand your ground as a professional or stand up for your profession. You replaced the boiler. Is the boiler functioning properly? Does it cycle on and off while maintaining the set temperature on the aquastat? Did you include in the wording of your proposal that it was the homeowner's choice to not replace any piping of the system beyond the minimal required to replace the old boiler?
You've bought this customer whether you like it or not. Now how much more are you going to pay to keep them? If you go back and find a way around the mess to get the air out you'll miss the one and only chance to fix what's really wrong. What happens the next time there's a problem and this customer blames it on something you DID? In their mind it's something you did, they will never accept the fact that the problems they're having are due to something they got you not to do in the first place.
This is all just my opinion and it's worth just that.
First I would point out (and prove it) that your boiler (which is all they paid you for) is working perfectly and that it's their system that isn't. Make them take ownership of the issue.
Make an offer to correct the problem for a price, being very wordy and careful to point out that every penny you'd be charging them is to replace or correct problems caused by the system that you connected to. Have it all in writing. You can price this fix at cost and write off the markup to education or if you had an original bid for doing it right in the first place offer to do the fix for that added amount.
You can offer to remove your boiler and refund all their money. Explain that they can then use their original amount to hire someone else to install a different boiler. Find a way to very softly remind them that the boiler is not the problem, but the original piping that they own.
You can bleed the system of the air that's trapped in it and then (good luck here) get them to sign off on the fact that this was a one time deal at no cost as part of the original installation, but any further issues with their heating system that are not specifically related to just the boiler itself will be charged at full service call rates. Remember, you didn't take ownership of the entire house just because you put a boiler in.
No matter how you proceed you need to come away from this having learned there are many definitions of: Getting the job at all costs. There are times we come across jobs that the little voice says "RUN!!!!!" From the pictures....... this was one of them if they were not going to allow you the profit to do the job right the first time.
Where is the air coming from? I'm assuming with 2 hours of purging and bleeding you had the system completely full of fresh water. Fresh water has lots of oxygen and other gases in it. Heat it up and all that air separates from the water and hangs out wherever it feels like it.
Piped properly, that air comes out of solution and gets trapped and vented at the air eliminator. The pressure out in the rads stays higher due to proper pump placement and air stays in the water until it comes back to the lowest pressure zone, right at the boiler.
Liberty, interesting and helpful thread, thanks for sharing.
Firecontrol, awesome layout of options!
Are there problems? Yes. Pump orientation is one. But guess what guys. That piping is not responsible for the air getting in the system. There are thousands of systems that pump into the boiler and into scoops. Guess what? They work. Is it ideal? No, but they still work. Pipe it like chuck shows and life is usually good.
Check the expansion tank first. Then, I would offer to repipe the boiler room, no charge. Do it like chuck shows, add lots of isolation valves. Isoflanges on the pump, valves on both sides of the zone valves, a valve then a drain valve on the expansion tank, Supply and return on the boiler.
Get rid of the di electrics on the pump.
Make it look nice and make it easy to service.
I'll bet he recommends you to other boiler owners.
I see one zone marked "basement". Is the basement zone an old radiant one, with copper in the concrete, or does any of the piping go into the concrete. If the answer is yes, then I will guarantee that there is a leak in the floor, which is where the air is coming from, either through the leak, or due to the constant introduction of water into the system, which brings oxygen/air into the system.
Also, that air eliminator would work better if it was straight up and down. Being crooked is going to prevent the float from moving up and down and releasing the air.