On Wed, 12 Aug 2009 08:36:21 -0700 (PDT), Lee Nowell
wrote:

We also have a microwave/ oven/ grill thing but the LCD screen stopped
working years ago

Was it a Sharp? I had a Sharp microwave oven and the LCD broke twice:
once under warranty and when it went the second time and the warranty
was up, I bought the panasonic because I needed to see the display to
see what I was doing. I made sure the replacement oven did not have an
LCD! I read some web sites after the event and Sharp microwave ovens'
LCDs had (still have?) a bad reputation for breaking.

luckily we only use it to warm food/ baby bottle

Naughty! I thought you were not supposed to do that in case of uneven
heating? That said, I know lots of people do

We moved the microwave to another room the other week and all of a
sudden it seems to be more efficient. A few times a day we warm water
for my daughters bottle in the bottle itself. So each time it is the
same volume of water and same size bottle. Anyway for the past 6
months, 40 seconds was fine (sometime 50 in the winter because the tap
water is colder!!). A few weeks ago, this seems to have reduced to
around 20 seconds!!! Whilst on the surface this seemed a good thing.
Should I be worried????

You have already mentioned water temperature, so unless it is that, I
don't know.