Hi D,
If you do not have an external thermastat, chances are that you have one of two faults, the first which is the simplest and will cost about £20 is the hot water pressure switch. Turn the main off. and only do this when the boiler is COLD!!!!!!!!
to locate it you will need to remove the front cover of the boiler, Philips screw underneath by pull out instructions. pull bottom of cover away and lift to the sky.
Next pull the clip on the right of the control panel away from the panel and allow the panel to unfold from the top, this will allow access to the boiler components.
if you look around the bottom of the boiler you will see a strange brass object at the back left, follow this across to the right you will see where it connects to the silver object (heat exchanger), so you should be looking at the middle of the boiler now, you have the gass valve infront of you, but just to the back left of the gas valve is a small black box that connects to the brass gear, this is the Hot water sensor! as you look at the bottom of it where it connects to brass you will see a black clip that holds it in place, you can release the clip by using a small screw driver, put it behind the clip vertically and then prize it off. the sensor will pull off to the right rear of the gas valve. now take your small screw driver and put it into the hole of the sensor (inside the rubber sleave) as you push it in you should hear a click this is a micro switch inside, if you do not, chances are you have just found the fault. to prove it, make sure you are safe and with the sensor laying safe turn the boiler back on, if it fires up again, its looking good.
Disconnect from the boiler and remove the back of the control panel, follow the two wires of the sensor to the control panel and pull of the connector. put the cover back on the control panel and try again, if the boiler does not perminantly fire you have found the faulty component, now find somewhere to get a replacement but do it in person and take the old one, as there are many different types.
to put the new one in is just the reverse, but turn the power off fully where it is plugged in, if it still has a plg remove it. the control panel uses 230Volts, enough to make you have a bad day!
the second fault could be a bent water pressure rod, not so cheap, but very unlikely. you will know this when you remove the pressure sensor, look at the rod sticking out of the brass unit, when the system is off it should be sticking out a little less than 8mm / 1/4 inch. if it is out as far as 15 mm / 1/2 inch.
you can either get another boiler or order the brass unit, which costs around £125 they do not sell the part of it, and chances are if it is a few years old the diapham is on its way out. I only say get a new one because I have had one of these boilers for 5 years, to date I have replaced the ignition unit, I had to rebuild the brass unit, and now I have to purchase a new gas valve. an expensive way to run a house hey!
I am not an engineer and I do not by anymeans endorse DIY repairs on boilers, but I know this one inside out.
Dave, July 2008
