Hi, I have just have a simular problem with my Ravenheat LS100T. The micro switch which is clipped to the valve body is operated by a pin which is connected to a diaphram in the end of the valve unit. When any hot tap is turned on. the pressure of the incoming cold water passing the diaphram pushes against the diaphram, and the pin moves away from the main valve unit. This pin is at rest under the micro switch, and keeps the switch closed, and the boiler will not fire up to heat the incoming cold water for hot water use. When the diaphram/pin moves under pressure, it moves away from a sprung loaded valve set-up within the valve body. This closes of flow to the central heating side of your system, and uses all the boilers heating aspect to super heating the cold water flow to your hot taps. The usual problem is that the diaphram fails (they only have a life span of 2 years!!). If this happens the cold water pressure has nothing to press against, urgo the pin won't move and the micro switch won't operate. by removing the micro switch from the valve you are effectivly manually activating the switch, and sounds like the switch is operating OK. If you have good heating under normal use, but your hot water is luke warm/intermitent, don't come on until tap half on or not there at all, I would replace the diaphram 1st, as a sure thing. It's a pig of a job, because there's not much room. You will need a new diaphram, fibre washers, O ring, little bit of water pump grease/silicone & lashings of Boss Blue + adjustable spanners, wrenches, tap wrench, etc. A universal diaphram is available online, which is about £13, and when you have it carefully remove the old pin from the old diaphram and replace the one on the universal diaphram with it. This saves time trying to cut the new one, as it will be too long and is made of a very, very hard material. Whilst you have the boiler drained you can replace (easy job) the two 'thermisters' (£7 each online), they are usually the next part to fail, they are both the same part number and interchangable. If you don't want to do the diaphram yourself, a plumber should be able to do it in about 2 hours. Valves are available online, but shop around/search, as I found prices up to £200 for the valve body complete!!. I changed all the parts individually, the found a valve online for under £70!!! so I got it for a spare. I did all the above, saved a packet and the boiler runs like new again. I hope this helps & good luck.
Matty, February 2010
