Baxi 105HE Hot water problems | Bathroom Advice | Plumbers Forums

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Aquariusplumb

Ok guys Iv hit a wall with this boiler. Baxi 105HE poor hot water, only lukewarm but choke tap down and it gets warmer but not exactly 'hot'. Pressure was quite poor as well. Iv checked the cold inlet for any blockage but was fine so I changed the plate heat exchanger which sorted out the pressure problem but still water only lukewarm. Had the heating on and boiler works fine and goes upto 80 on front panel. Put hot water on and boiler only goes upto 50 on the panel. Iv shut down both isolation valves on heating when hot water was on so it wasn't dumping down the flow. I then took the board out and zeroed the dials incase it had previously had a new board not fitted right but that wasn't the issue. Iv checked the dhw sensor which was right 12k ohms at room temp dropping down to about 6k at 50 on panel. Gas rated the boiler in hot water only which came out at 28.9kw and my burner pressure was 12.51mbr so to me the boiler is working flat out exactly as it should yet can't get the temperature past 50 on the panel. Had a spare pcb on the can so tried that but still got the issue so took that back off. Heating side water is pretty clear as magna clean gets checked and inhibitor with every annual service. The boiler will continually run with the hot tap on but won't go over 50 on the dial and water still doesn't heat up as it should. Only pumping out 9/9.5 lm. I do apologise about the lukewarm comment but I couldn't find my stat in my bag. Obviously the boilers working exactly as it should trying to heat up so my last thought was that a mixer tap/shower must be passing cooling the water. Any ideas are a massive help. Thanks
 
No it's running at max as its not heating up enough. Should have 35'c rise at 12lm. My thought was the heat has to be going somewhere as it will just run and run. Left it for 8/10 mins and always the same.
 
Can't be internal bypass then if it keeps going. You need to check from cold that's it's not going down heating. Isolating valves may not be enough if they aren't shutting off properly.
Also check exactly what temp rise you have. Other than that I would ring Baxi.
 
i had exact same problem on same boiler other week was only getting lukewarm water, did all tests your saying, was about to give up then customer mentioned about new mixer shower hubby had put in and when i checked it found hot and cold pipe in mixer shower were crossed causing the same symptoms you are getting.
 
Ok so Iv been back to this and it's a real head scratcher. I changed the flow regulator and Venturi in the inlet manifold. Boilers in the loft, turn kitchen tap on and boiler fires up and pumps out 48'c all day long. Turn bath tap on and you get 31'c. Choke the tap down and you get 48'c but then it filters back down to 31'c. I get a 38'c temp diff across the cold and hot when the kitchen tap runs but I only get 19/20 across when bath taps on
 

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