Junkers WR11 G... WR14G... Are there any UK based outlets were I can opbtain spare parts and english written manual.

the low pressure/flow minimum is for safety and protection of unit and no adjustment to do so

they all work the same
http://www.americanwaterheater.com/support/manuals/res-gas.pdf

Is it gas or electric? if it is gas and has a pilot, and the pilot is out. If you don't smell gas go through the start pilot proceedure. when the pilot is running it produces a small electric current sufficient to hold the main gas valve open; then the temperture sensor allows the unit to keep the water heated.

Do NOT disconnect anything. Has the unit been maintained, cleaned and serviced? There may be a limit switch malfunctioning. Your safest bet is to have it checked out my someone who knows and is familiar with the unit you have, could be simple, but be safe and have it looked at.

1) Web search 'WR11 water heater .pdf' shows Bosch WR11 manual
http://www.boschsupportline.nl/content/files/TechDocs/Geisers/6720607884.pdf

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

http://documents.junkers.com/download/pdf/file/7181465057.pdf Sometimes there are several parts on this model to find buit beware on some marketing technical made differences inbetween one year of build there can be some modifications inside.

Succes

first find out from your manual what the flashing red light means...that should narrow your search---could be a thermocouple shot,a rubber diphragm in the gas valve has weakened and not operated, or gas pressure into the appliance may suddenly be too low, or springs in gas valve may have worn out---very many possibilities

Yes that is going to be the contoll valve on that heater. You can probley fix it very easy with the right part. You will need to locate a plumbing supply over there in the UK. Give them the make and model number and tell them you need a unitroll gas valve for it.