My alpha 280e combi boiler has a problem with the hot water temperature, it fires up ok starts to heat the water then the burner stops and water runs cold.on inspection inside i noticed that both the hot water and the central heating pins extend out of there diaphram housing to trip the micro switches firing the boilers burners.i have changed the diaphram in the hot water diaphram housing as it had a small leak of water coming from the pin.I had a simular problem with the boiler only about 14 months ago when the plumbers changed the diverter valve, if it is the diverter valve again i can change it again but I would have thought it would have lasted longer than 14 months.Could you give me a idea if it is this or somthing else, many thanks.

Tony, January 2006

Mike you were spot on. it was the hot water temperature sensor. it cost £15 from a parts dept. sorry for the delay in the reply, Iam crap with computors and did not know were the website was that I asked the question on.

tony, June 2010

I think its worth getting a decent boiler to begin with. I had the same problem three years ago, and i change the diaphram etc etc. Soon again same thing happen, then i realised its the water pressure .... too weak, so its cutting out on overheat - I'm guessing here but i assume your combi boiler is situated upstairs in the house.

I got around it by removing the solid cap but remembering to completely disconnect it as its manegtic and you break it if you just left it. I then screwed in the danfoss valve (The bit which the magnetic solenoid cap sits in) in or out with the hot water running until I achieved it more or less hot ... not scholderingly hot.

It worked for me and its been ok since for 3 years now.

Goodluck.

Chan, February 2010

where can these sensors be bought from , as the plumber that changed mine about 18 months ago said the part was £25. As above I would've expected more life than 18 months (gone again yesterday-see what he charges me this time). If I can keep a couple spare I'll be prepared in future. Any suggestions of suppliers appreciated. Thanks

clarecafc, July 2008

please copy & paste this into other forums.
The pin goes through a "nylon" section on the diverter valve. within this section is a "tiny" o'ring.. this O ring & the nylon section are worn. Boiler manufacturers know this but fail to supply these parts as there is more money in a new diverter valve than supplying a tiny o ring.
so how do you fix the leak, well I removed the cover off my valve, placed some grease in the o ring with a fine screwdriver, then hit the nylon section (at both ends) with a hammer & bolt (the bolt was the same diameter as the nylon at the outside end) & the inner section ov the cover plate I hit that with a larger diameter bolt taking care not to over hit it or damage it in any way. While doing this a few times & checking the diaphram pin is still free to move in & out.
Resullt: I basically squashed the nylon into the o ring to make a better seal round the pin..OK

R Walker, June 2008

i have the same problem detailed above.i too have changed the hydraulic pressure differential assembly and the domestic water heat exchanger but am suffering the same symptoms.any ideas would be much appreciated.
dominic

dominic adam, August 2007

could b but change the hot water temperature sensor first relatively cheap around 10 or 15 pounds

mike, January 2006