Baxi combi 105e dhw fault

Hi,

I was wondering if anyone could help. My Baxi Combi Instant 105e has developed a fault over the past week or so.

The domestic hot water works fine, but occasionally, the central heating won't switch in.

When the fault occurs, all of the red temperature neons are lit (none flashing) and the power and domestic hot water neons on the row below are lit (both solid, not flashing) and the pump can be heard running. The hot water continues to be hot and work okay, but the heating does not cut in.

I have to switch the boiler off and on again, and then everything seems to work okay for a while, until it starts playing up again.

Does anybody have any idea what the fault might be?

Many thanks for your assistance.

RichM

Hi,

Does anyone have any suggestions about this problem, please?

RichM

sounds like it's sticking in hot water mode so it'll not tell the diverter valve to move into ch position. Pretty common on the instants. Usually not the dhw diaphragm section that sticks but the pin inside the section behind it. You can test the theory by removing the dhw microswitch and seeing if it goes to ch after dhw preheat (flashing dhw light)

Drain the dhw and ch sections of the boiler, remove the dhw diaphragm section by undoing the 2 copper pipes (careful with the fibre washers!) and pulling the clip out from behind it. You can remove the front of the diverter section (which is a pain in the erse to get a spanner into, I use my rothenberger tap spanner). Clean the pin with some wire wool, grease it with a little silicon grease and re-assemble. You may find the large o-ring may need a wrap of thread tape to reseat without any leaks. If it looks like there's been water seeping through the pin is it's better to replace that front section. Baxi don't do it as a spare part but it is available from ideal as it's the same part on the ideal Mini C. I don't know the part number but it's described as a valve service kit.

Many thanks for that weargas,

I'll have a look and see how it goes.

Regards

RichM

Thanks weargas, you were absolutely spot on.

The pin behind the diaphragm had some limescale on it and a quick outing with the wire wool made it as good as new. It was also really easy, and I wonder if my model of boiler is slightly different from the one you were referring to. I simply had to drain down the dhw side of things, undo one copper pipe (looking out for the fibre washer - thanks for that advice), undo 4 screws take off the front of the casing and I was then able to remove the pin behind the diaphragm, without disturbing the diaphragm itself.

Many thanks for your great advice.

I'm off for a hot bath now.

RichM

The whole assy you stripped actually comes away from the rest of the valve by removing the black clip behind it. The pin I was referring to is furthur behind the one you did but if you've got it working I guess you picked the right one!