Ok, finally sorted it, with much help from daftlad.
I now have my cold fill machine working with hot and cold water.
This is the layout of the plumbing inside the machine (Hotpoint WF545 ‘Aquarius’):
Luckily ,as you can see, I had a blanked off inlet to the drawer that goes straight to the main wash section, there was also a nice little space on the back of the machine marked ‘H’, next to the ‘C’ (cold solenoid). So obviously its all pretty identical to a H&C fill machine they must produce too.
What happens when the machine runs is that the prewash side of the solenoid runs for about 10 seconds, just rinsing the pre-wash drawer out.
It then stops and the main wash side of the valve opens up, on and off, for about 4-5 minutes.
When it needs to use the softener, both valves open and the combined water from both jets hitting each other forces it down the middle channel and into the softener section.
So with daftlad’s advice and assistance I have added a DPDT relay (
http://www.maplin.co.uk/module.aspx?moduleno=37518), a switch (
http://www.maplin.co.uk/module.aspx?moduleno=2504) and a 7 minute timer (MK Sentry Time Delay switch – ebay £6).
Basically I fill the machine and add detergent/softener as normal and then I run the kitchen hot tap to prime the pipework with hot water (I’m lucky in that my machine is close to my kitchen sink and they’re both close to the hot water cylinder, so I can prime the pipework with hot water easily and quickly),
when it’s hot I turn the machine on, press my new button and then the programme start button.
While the timer is activated the relay switches power off of the pre-wash valve (to stop any cold water from entering the drum) and switches the power between the main wash valve and the new hot valve.
So for 7 minutes the machine only has access to hot water. After that it switches back to normal and will rinse in cold water.
Doing this has cost me about £21. The machine is meant to consume 1.14kWh per wash ( I don’t know which programme/temperature though), using our solar water it consumes 0.12kWh on a 50C colour wash ( I assume it’d be the same for any temp wash as long as the incoming water is far enough above the dial temp to counter the cooling due to the machine)
At 9p per kWh and doing 4 washes a week it should pay itself back within 2 years (taking into account winter where we may not have the excess hot water). If electricity goes up, it’ll payback sooner, and if the solar performs well during winter it’ll also payback sooner.
Final circuit diagram and photos to follow in the morning...
