Baxi DuoTec 24 He Hot water problem

[Whizzard17]

Hi. Boiler is three years old. Noticed recently that on full flow - from kitchen and bathroom tap - that water does not come as hot as it should. When flow is reduced, temp increases on both so filling the bath takes a little longer! I have set the temp at 60degC and on full flow forom either tap, but display show actual temp at around 50degC. I used a thermometer and actual temp from tap was 34degC. Flow rate measured at around11.5l/min and 10.5l/min at kitchen and bath tap respectively. (Measured with a bucket and stop watch as I don not have a weir gauge).There are occasions when the actual temp is showing 71degC but I cannot confirm the temp at the tap as only have a medical thermometer which just reads 'HI' beyond 42degC! I have gone through the fault finding in the manual and could deduce from this that it could be the NTC sensor or heat exchanger. I have inspected the heat exchanger visually and looks ok and clean. Pump and fan run and stop in correct sequence when they should do. I don't want to have to call anyone out if it's something I can do myself. I'd grateful for any help. Thanks

WP_20171123_11_36_43_Pro

• Whizzard17
• 24 Nov 2017

 

[Gasguru]

Probably nothing wrong..

The spec for that model shows it will raise the temperature of the incoming cold water by 35 degrees at a flow rate of 9.8 litres/min.
For example with a typical incoming cold water temp of say 5 degrees raising it 35 degrees would give a lowish bath temp of 40 degrees and this is only possible if you drop the flowrate down to 10 litres/min. Exceed that flowrate and it can't raise the temperture sufficient for a hot bath/shower....therefore turn the flowrate down to get hotter water.

If you really want to check the boiler is operating properly there's a couple of simple checks...

let the radiators become cold, turn on all the hot water taps and feel the flow pipe (LHS 22mm pipe) about a meter away from the boiler. If it gets significantly hot you have a diverter valve fault.

have a look at the FAQ section and gas rate the boiler with all the hot taps fully open and hot water temp on boiler at max. Compare it with the figure in the manual...use the meter cubed figure (it's the most accurate).

A 24 Kw boiler is the lowest spec model and at this time of year a bath can easily take 10 to 15 minutes to fill.

 

[Whizzard17]

Hi and thanks for the info.I wasn't able to check heat on the flow pipe as it's set behind kitchen units. However I did make some calculations on the gas. After 2mins,from the gas meter, there was of difference of 0.0782m^3. So divide by 2 and multiply by 60 gives 2.346m^3/hr. This equates to 82.98ft^3/hr= 86297 btu/hr = 25.29kW. Manual shows gas rate of 2.61m^3/hr (over 10 minutes). DHW heat input Gross/Net are 24.7/27.4 . Output is 24kW. I guess according to these figures, everything is good However, I don't understand why when set to 60degC, the display showed a temp of 50degC but measurement at the tap was 34degC.Aside from this, all else seems logical.

 

[Gasguru]

Feel the heating flow pipe under the boiler...but take into account that it will heat a little through conduction.
The gas rate appears to be ok.

As well as drawing off water at too higher rate to achieve the required temperature perhaps you also have a mixer tap problem..ie. although you are just opening the hot tap you may find cold water is also being blended in via a faulty mixer valve on either that tap fitting or elsewhere on another mixer tap/shower. Isolate the cold feeds to taps to confirm.

 

[Whizzard17]

Hi and sorry for getting back so late. Been under the weather . Ok so I have checked the heating flow pipe and it indeed gets quite hot when radiators are off. Guess I have a diverter valve problem. I'll have to check the warranty. It's over three years now. Bit annoyed really. My old Vaillant went 25 years before I had to start changing bits. Many thanks

 

[gas112]

if someone who is registered with baxi installed it then it is 7 years if not only 2 years warranty

 

[Whizzard17]

Yep. He is Baxi registered and all services by Baxi registered engineer. Thanks for that

 

[Whizzard17]

Just realized I hadn't updated this post! (Apologies because you guys spend your time helping us out). Baxi engineer came round and changed DHW ntc sensor and diverter valve. Said common problem because no filter fitted on heating return.Covered under warranty because problem was identified after. Newer installs will have another filter fitted. Cheers all.