I have a Mitsubishi WP-105QS water pump that is losing air in the pressure tank after about 2 or 3 weeks of operation. When it was new, the pump would cycle on and off after dispensing several litres of water, but now after 2 or 3 weeks of operation, it cycles on and off after dispensing only about half a litre of water. To overcome the problem, I shut-off the water pump and water supply, open the pressure tank drain plug, drain the water, and then open the water intake and turn on the pump, re-balancing the pressure tank.

 

How do I fix this? Anyone else experience this?

 

 

Moving to the DIY forum. 

The problem that you described is called a "waterlogged" pump.  I have 3 Mitsubishi pumps and it occasionally happens and is caused by the air/water imbalance in the tank.  The Mitsubishi pumps do not have an internal rubber bladder and the air balance is controlled  by the AC Assembly, item 19, in the IPL.  you could try taking it apart and cleaning it or if defective you could replace it.

 

I buy all of my parts from Kang Yong Wattana, https://www.mitsubishi-kyw.co.th/contact.php?lang=en, in Bangkok.  

 

In fact the last part that I bought was an AC Assembly for my WP255Q3.  I ordered and paid for it on Monday and got it EMS on Wednesday.  Cost about 650 baht.  The IPL that I attached is for WP200 series and up.  If you email them they will send you an IPL for your pump so that they are sure that they are supplying the part that you need.  The problem with my pump actually turned out to be item 21, pipe-AC, somehow the lip had deteriorated and the pie had fallen into the tank.

 

Since I can't attach emails, PM me and I will send you the email address of my contact.

 

WP-255Q3 IPL.pdf

I contacted one of the guys you recommended, described the issue and received the attached IPL. The guy recommended buying a new tank, part 

24

TANK ASSY WP-105

H01401J01

1

1,567.55

I doubt there is a hold the tank assembly.

 

The tank is just the tank, none of the other bits attached.  The last one that I bought was for a WP-255Q3.  It cost about 2400 baht delivered EMS to Nakhon Sawan.  I really don't see the problem being the tank but they're the experts.  My tank was replaced due to a small leak at one of the welded stiffeners for a water connection.  I replaced one on a WP-155 a few years ago with the same problem.

 

If you do but the yank when you take the old one apart don't forget part 18 - it looks like part of the tank.  If you do, your pump will definitely keep turning off and on.