Electrical Immersion Heater - Boiler Mate II

Hi,

I have a 9 year old Boilermate II in the house we have lived in for 4 years fitted with both a pipe based anti-scale device and a main water softener. Over this period all I have ever altered on the unit is the quirky summer/winter thermostat dependening on the season - it has always delivered adequate heating and hot water for our 5 bedroom/3 shower/1 bath house. However over the last 6 months, like many individuals here, we have noticed there being less hot water being available and often going tepid before a shower is completed, or a bath adequately filled. The heating remains fine. I therefore suspect some form of water scale-contamination (believe it or not I had a Boilermate II in my previous home that need a new heat exchanger after 2 years from new due to scaling).
Therefore I'm likely to get a Gledhill specialist in to give it a proper inspection.

However before doing so I have taken a closer look and mine appears to be fitted with an electrical immersion heater on a seperate socket (the operating manual seems to indicate these are optional?). The socket has been switched off since the day we moved in. Whilst I doubt switching it one now will remedy the cooling of the hot water, I can't find any guidance in manual as to when this immersion should be used? Given we've always had a ready supply of hot water I have been reluctant to turn it on / leave on permanently in case there is no auto on/off trip and I'm simply burning electricity for no real benefit?

Therefore I'd be grateful for any advice on the correct usage/setting for the electrical immersion for when the BMII is fixed.

immersion is for emergency use only., eg your gas supply is interupted or gas boiler faults, it can be switched on for heating /hot water but it is expensive 3kw per hr until it reaches temp.
hope this helps
mark,
www.gledhill-repair.co.uk