Baxi Duo Tec wrong temperature reading for hot water

[SeeYouThere]

Hi,

I'm having problems with my Baxi Duo Tec Combi 28 HE A. I noticed it first in the shower that the water was going hot-cool-hot. Looking at the temperature gauge on the boiler it is reading incorrect. The temperature gauge is set at 60oC but even when the water is cold it's reading around 50oC and when at what is proably around 60oC it is reading 90oC which it clearly isn't as you can hold your hand under it. So when the hot water tap is on it shows it going up to 90oC then the flame goes out and it cools down to around 70oC, then the flame comes back on and it just cycles between what it says is 90oC and 70oC, althought the boiler is set at its maximum of 60oC and in reality the 70oC is probably around 30oC.

So I thought it would simply be the temperature sensor for the hot water. Took it out and cleaned it and no better. So then I got a new temperature sensor and still have the problem. Can anyone shed some light on what it might possibly be? I should also say that the central heating appears to be working fine.

Thank you for any help or suggestions.

 

[Baxmax]

Blocked plate heat exchanger.Remove clean out or replace

 

[SeeYouThere]

Ah that makes sense. I now realise that the temperature reading is for the water in the primary circuit before it goes into the plate heat exchanger and not for the temperature of the hot water to the tap! Thank you very much for your help. I will drain the primary circuit tomorrow and remove and try to clean the plate heat exchanger.

 

[SeeYouThere]

Just to update - Today I isolated and flushed each radiator in turn several times until the water ran relatively clear. I then removed the heat exchanger. First I flushed with a strong hose and this removed quite a bit of black crusty stuff. I then soaked in descaler which seemed to loosen up more black stuff which I again flushed out and repeated several times. I also banged the heat exchanger carefully but firmly against a piece of timber which definitely helped to dislodge more black stuff. I also ran boiling water through the heat exchanger. With the DHW now set at 60oC the temp of the boiler runs around 70oC so it looks like the combination I used to clean it did the trick . I've now added cleaner to the central heating system and will leave for 3 weeks and then flush and add inhibitor. I might also give the heat exchanger another clean at that time if I feel it might need it as it was an easy job to remove it and put it back - just a case of opening two screws - luckily it sealed back fine without having to replace the seals.