need assistance with baxi luna operation

[SuperSewist]

The company I bought my -- BAXI LUNA 301fi -- from in 2004, whom I believed was a reliable dealer, no longer sells or services this brand , and neither myself or (allegedly) my plumber (and installer of it) has been able to find tech support despite MUCH effort over the last six months. Not even from Marathon International. I have not been able to find any one who will work on my BAXI. I've pretty much been told I'm on my own to troubleshoot. Although that is a common thing here in Wyoming. I have no problem doing plumbing stuff, as long as I have a clue, and I'm not (too) afraid to take things apart. so here goes:

the heating system works fine although it is excreting about a quart of water a day through the pressure relief outlet and I don't think that's right.

the DHW is not making reliable hot water. It will be nice and hot and then go cold for no (apparent) reason. Or, not be hot at all until a second tap is turned full on. We have good public water pressure here so 3.5gpm should be no problem. Or, it will be making nice hot water, then you turn on just a little cold to regulate temp at the faucet, and the whole flow goes cold. I have replaced the "pressure differential assembly" with no change in symptoms. However I can say that I have visually confirmed that the DHW pushrod does not "push" when one tap is turned on but does when two are on.

My plumber has told me he will not work on it any more other than cleaning and annual maintenance without a tech support person to call. I have begged the seller for support but no dice. So here I am with tools at the ready along with my trusty owner's manual and a mop . And hopefully a clue from one of y'all as to what I am looking for. **I have a wrench and I know how to use it. I'm just not too sure what to use it for**

As always, TIA for any advice or suggestions.

[jadnashua]

Your expansion tank may be waterlogged, and replacing that for maybe $30 or so may solve the T&P relief issue. If when you tap on it, it sounds like it is full of water, replace it. If you check the air pressure and water comes out, another way to check, it is shot.

As to the rest...can't help.

[nhmaster]

Win-Air company, Laconia New Hampshire sells Baxi.

[SuperSewist]

Response from win-air was to call marathon intl which had already proved a dead end for me. Replaced expansion tank, thanks. So then I called every plumber within 50 miles, not a one of them had even heard of Baxi (?!) but I did find one who was willing to give it a go. After some learning curve with the manual, he found a plastic filter screen that had apparently deteriorated due to our local water supply having something in it that is hard on plastic, it had crumpled inside the piping to cause blockage. Other than parts taking 18 days to arrive during which time there was no hot water available, it seemed to be a straightforward fix. Hot water abounds and now I know there are 3 filters to check, not just the two that are easily accessible. The third one requires removing the pump to get to it. Thanks to you all for giving me the shred of hope I needed to keep after this until I found a tech, who is now my new favorite plumber!