My Hitachi GX series WT-P 300GX2  starting to act weird. After 5 years without any problem. Now suddenly it was running all the time.

To get it back to normal had to bleed air, and there was a lot of air.

Then it lasted for 14 days and same procedure bleeding air again. No leaking pipes or any other signs of problems in the house.

I checked all over Internet but could not find any good suggestions for my problem.

Contacted a specialist in Bangkok and he new exactly what it was. He changed the "Head chamber" and when he got old one out he showed me

what the problem was. See picture I attached  ..._160407.jpg showing that the plastic inside head chamber is broken.

Easy  to fix yourself if you can isolate the pump and parts can be bought at Lazada.

Very good post. Not as rare of a pump issue as one would think. The OP was sharp to contact Bangkok and find the solution.