Am looking for some help with an issue on my Baxi 105e combi boiler. Will try to give as much info as possible. CH works fine at all times. Boiler situated in downstairs cupboard. When there is a demand for DHW the hot water will heat for a while before going cool and then repeating. It has progressed from giving hot water in this fashion to lukewarm at bestto the taps upstairs. Having watched the display while running the tap the following happens. Registers a demand for hot water, fires up, heats the water. Display shows temperature up to 80 degrees. The boiler then shuts off, the cold water running through lowers the temperature, the boiler fires up again and repeats the process. I have tested things a variety of ways, here are some of the other symptoms: Regardless of whether the CH is on or not 3 out of 4 of the upstairs rads get extremely hot while running DHW. The issue seems to be prevalent for upstairs DHW only. If I run the downstairs HW there are no obvious problems - Downstairs HW is lower in height than the location of the boiler (not sure if that is significant). Having removed the front panel, the diverter does appear to have some scale running round the right hand side. Would appreciate any advice.
Blocked secondary heat exchanger....remove, descale and refit with new lip seals. Also service the hydro block inner valve assmembly while your boiler is in bits. Should be able to do this without removing the gas valve.
Totally agree with all above, may also pay to replace the thremisor whilst your at it, these ones have a habit of having an anoying weep on them ususally covered in crust.
Thanks! Straightforward or complicated job? I'm competent in terms of DIY/mechanics so is this one I could conceivably do myself? How expensive if I get someone in - I only ask because typically this has occurred at the same time as tax/mot/insurance and unexpected vet bills last week...
Its not difficult, and it is fully described in the installation instructions. You will need to get the new thermistor and O rings and washers from somewhere like Parts centre. You will also need some Fernox DS 3 which comes as crystals in a tub. They work better in hot water from the kettle. Do wear some latex gloves whilst your handling this stuff as its corrosive. Also have a few old towels to hand when you do it as these boilers never fully drain and there is always a small gush when removing the plate heat exchanger. The thermistor will need a 13mm spanner.
While doing this it is also best to change the DHW Diaphragm as well. They are cheap and easy to do. Use plumbers grease on the spindles. The seals come with the kit. There is also a pump proving diaphragm. If all is being stripped out replace this as well. When all is stripped replace the expendable parts, then you will have a trouble free combi. These combis are very reliable and are pretty easy to work on. When all done. Every year put plumber grease on the two moving spindles on the DHW valve and the pump proving valve. The grease eventually works its way down the spindle into the seal ensuring a long lasting seal.