Moen Posi-Temp Shower Occasional Lukewarm vs Hot
Our furnace 'seems' to be working fine regarding heating the home, but our upstairs shower over the past month or two often only has lukewarm hot water. It DOES seem like it's on colder days so perhaps it's working hard heating the 5 zones of the house. I've moved the thermostat schedules earlier in the AM so the heating wouldn't conflict but it is still occurring.
Some of those instances the downstairs kitchen sink & shower were plenty hot, others they were lukewarm as well. The Posi-Temp has not been adjusted (or cleaned) in 6 years since we moved in.
Reading other Q&A's on similar Moen's, it appears not to be a cartridge problem as there isn't a leak. The Posi-Temp hasn't been adjusted so that shouldn't be the case.
So I've narrowed it to these:
1. The coil has AGAIN become encrusted with Manganese. We've acid flushed it 18 months ago as it barely allowed ANY flow of water through coil. A 1 micron filter was installed but some managanese still exists as every few months it keeps clogging shower and drain screens. Plumber at the time advised the acid would 'pit' the coil and the situation WOULD return but had no idea of time frame.
2. Posi-Temp cartridge/scald setting ARE contributing to the situation.
3. Copper pipes to upstairs are either narrowed due to years of manganese build-up or pipes are partially obstructed by an object.
4. Furnace simply cannot keep up with heating duties AND shower flow (but why only / most often) to upstairs bathroom?
Plumbing service call rates in NH are OUTRAGEOUS (including the travel time they charge, it's about $300 to JUST SHOW UP) so I'd like to identify/narrow the possibilities before I call them again.
I'm leaning towards the coil (#1) and preparing to replace it. Before, I'm planning to put a bucket under the drain valve, open it full blast and see the outflow. When the coil was acid flushed before, they could BARELY get a sputter of acid through.
Can I hurt anything by doing this?? :confused:
Thank you!