Electrical – Can i get electrocuted with boiler

When the boiler is running (especially in heating rather than hot water mode) watch the pressure gauge: does it rise almost all the way to maximum? And do you then get a sudden discharge of hot water through the pressure relief discharge (PRD) valve and pipe to the outside of the building? (If the boiler is mounted on an external wall the PRD pipe usually goes directly through the wall behind the boiler.)

If so this is where you're losing water (and hence pressure). It indicates that the expansion vessel (probably built-into the boiler) is faulty. It may just have lost pressure (there's a Schraeder(sp?) car-tyre-style valve you can use to top it up) but could have failed entirely (e.g. if water comes out of the air valve!). For expansion vessels built into boilers it's often more trouble and expense than it's worth to replace the fitted one and quite acceptable to fit a vessel externally.

The uk.d-i-y usenet newsgroup is generally a good place to discuss this sort of problem. There is also a wiki/faq at http://wiki.diyfaq.org.uk/

I've not used a system like you have, but I'll give you some information based on what's common for heating systems in the UK.

As you've discovered, the immersion switch immediately switches the heater on. It's usually used as an override when you want water to start heating outside the timed period. (I'd hazard a guess that having the immersion on for 10 minutes won't be long enough to heat sufficient water for a shower).

You'd usually set the heating on timed, but it will take a while to heat up the full tank of water. For example, if you get up at 07:00 and have a shower, you might need to set the timer to come on at 06:00 to give you a tank of hot water ready for when you get up.

It's common to set the timer to come on twice a day, so you get hot water in the morning and again in the evening - though you'd adjust that dependent on your usage pattern. It might take a little experimentation to find out when you need to set the timer to come on to give you the hot water you need.

If the T&P valve is flowing quite an amount of water, it sounds like something is amiss with the system.