It is not a welded contact, That is the design so that it fails safely (hence a Failsafe circuit) When there is any question on the reading from the pressure switch on the board, the pump is turned on to prevent any overflowing or flooding. There are, as others have mentioned, a huge batch of bad switches from Panasonic. It has nothing to do with the design of the board. I have repaired many with the same part removed from nearly identical boards built 10 to 15 years ago. ( machines that died from other reasons. )
One of the things that has annoyed the hell out of me is the use of "tact" or "Tac" momentary contact switches in electronics.
Sure, they're compact, they control signals to the microprocessors, etc.
And they only require a light press to operate.
But they're not as durable as old school switches.
And they're a pain to replace if they become faulty.
Careful unsoldering and replacement is mandatory.
Believe me, I must have replaced hundreds of them over the years, in stereo equipment, among other modern equipment using them.
But they're cheap enough to purchase. (part of the cost-cutting of manufacture)
They also come in different length buttons for a given design panel.
Mouser, along with other parts distributors carries replacements, Panasonic being one supplier they carry.
I have to put an order in to them when I get the time.
The internal contacts eventually build up tarnish on them, or corrosion due to airborn issues, causing them to become difficult or impossible to actuate.
People then push them harder to force them to work, causing other problems with the equipment their in.
I'd assume the humidity level in a washing machine or dryer can accelerate this problem with them.
A short button version....
