Overheating & Ripoff

[GreyVanMan]

Long story, trying to keep short.
120miles into journey, van goes into limp mode, no visible warnings on dashboard.
Cooling water reservoir empty, water everywhere. Cool down, top up from kettle. Limp into nearby dealership (lucky - maybe not!) Yes we can fix that!
Dealership diagnose thermostat, replace, still overheating, possibly waterpump, BTW £790 please.
Recovery: assessor has a look - turn engine on, turn on cab heater - no heat - 'It's your water pump gov'nr', all inside 60seconds.
Recovered back to Cornwall. Fixed at my favourite garage, yes, it was the water pump. Basic.
I am considering taking action against the dealership: They misdiagnosed the problem, carried out unnecessary work, and fabricated a bill of £790.

My question is; am I wrong is claiming they should have been able to properly diagnose the problem by use of the heater?
If they didn't know this, they should have known it. The basis being that no matter what the thermostat was doing the heater will still work, if the water pump had failed there would be no water circulating to reach the heater.
I have approached the dealership who refute my claims and request for refund (partial).

 

[Barriesimpson]

Not quite sure what you are trying to show me because most vehicle mechanics & engineers will know that there was, at least, two types of thermostat.

The thermostat is often operated by air pressure or vacuum in the bellows surrounded by or contained inside by a large spring,

Should the thermostat fail, this large spring forces it into the open position.

If you know any different, could you please either show a link or better still, post a picture because I'm always open to be educated and in 65yrs of spannering on ships, boats,cars, trucks and coaches, I have never seen one.

It just doesn't make sense that any machine thermostat would fail in a closed position and cause that machine to overheat!

Well if you have the bad habit of using tap water rather than an antifreeze solution in the cooling system, the rust and gunk that will be created can and probably will weld it shut (for want of a better terminology). I have seen it happen a few times in my also 'many years of spannering', as you so eloquently put it . However, as you and many others have said, the most likely is that it will fail in the open position and the running temperature will never be reached.