duo tec hea

[buckley plumb]

if i have not got enought of my own boiler problems the guy i sometimes help out called last night - a customer of his has complained the water is not as hot as it used to be . he spoke to baxi and they advised changing plate and hw thermistor which he has done and still the same - they then said gas valve and he did - boiler still the same .he said on htg the flow pipe gets to 80 degrees but when on hw full flow the flow pipe only gets to 53 degrees (60 degrees if tap reduced to half flow ) i have never checked the flow pipe on a boiler when in hw so not sure if this is ok it could be good heat transfer to the water in plate and good circulation) i told him to test the cold water inlet temp and the hot outlet and if hes getting a 35 degree rise then the boiler is ok . also check the htg thermistor / work press / gas rate /. anyone know what temp to expect on the flow pipe in hw mode i assume it should be above 70

 

[leethegasman]

In cases like this first thing I check is flow rate of hot water cold temp hot temp = temp rise have had a few cases and it just can be mains cold water supply colder in the cooler months if all readings to MI no parts will make it hotter, there may be other checks you will sone get more answers on here

 

[zeebeedee]

Can't remember if the boiler has a control for the hw on the front? Has this been turned down then snapped stopping it actually turning it back up in the board? If he has changed the plate thermistor and gas valve I'd be looking towards the board

 

[buckley plumb]

he just called me and i talked him through a few things - he said cold water is 15 degrees and hot water out 45 degrees full flow so its not to far out from the 35 degree rise advised to check flow rate but he did not have flow cup boiler temp on display for water shows 45 if he turns tap down to half flow boiler display for hw shows 60 so i think he has a to much flow or just the temp of the cold water - but customer addimant its not been like this before going to look monday evening

 

[leethegasman]

If no flow cup time how long it takes to fill a bucket as long as you know how many litres it holds you can work it out you can get flow cup from Plumbfix think mine was about £15.00

 

[aggis]

May well be worth looking at the pressure 1st, even if the flow rate is correct, but pressure too high, you can have poor performance, because the waters going thro' too fast. Manufactures usually test the boilers at approx 2 bar w/p.
Also usually when it's a w/w plate hex problem, it's caused by a blockage & when that's happened it's due to dirty/sludged system. Always recommend the system to be flushed or if they're not willing to do that, write it in your report, then when it blocks again, you're covered.

 

[Billy Bob Bob]

sounds like nothing wrong with the boiler taps being run to fast

 

[buckley plumb]

sounds like nothing wrong with the boiler taps being run to fast

my thought as well will let you know when ive been monday evening

 

[stevetheplumber]

May well be worth looking at the pressure 1st, even if the flow rate is correct, but pressure too high, you can have poor performance, because the waters going thro' too fast. Manufactures usually test the boilers at approx 2 bar w/p.
Also usually when it's a w/w plate hex problem, it's caused by a blockage & when that's happened it's due to dirty/sludged system. Always recommend the system to be flushed or if they're not willing to do that, write it in your report, then when it blocks again, you're covered.

how can the water be to fast if the flow rate is correct? flow is flow and pressure is pressure if the flow rate is right the pressure has no effect

 

[BLOD]

have to agree with steve - if the boiler's designed to heat (eg) 12lpm with a 35 degree rise then pressure has nothing to do with it - it's about flow rate

 

[aggis]

Pressure & flow rate.
The pressure pushes the water thro' the heat exchanger, so if the flow rate[ which is the quantity of water ] is going thro' too fast it doesnt make the correct temp rise,

 

[dancinplumba]

if its going thro too fast then the flow is to great, nowt to do with pressure !!

 

[buckley plumb]

been to it just. htg is fine .put in hwmode and the flow pipe from heat exch gets hot then boiler modulates down . in hw mode slight leakage of heat down flow and bypass pipe warm . removed the diverter motor thats working fine and then rermoved the diverter gland but only the
top half comes out - can press bottom part with my finger but not sure about the seals on the bottom part.cleaned top half and re assembled and still the same . my mate put new plate on and hw temp sensor and for some reason a gas valve . sure its diverter now - can you get a repair kit for this also is the by pass pipe just an open pipe or is there a press sensitive part in the diverter

ant

 

[Billy Bob Bob]

no repair kit available sadly

 

[buckley plumb]

no repair kit available sadly

would you agree diverter - puzled me as i turned off the htg flow and rtn iso valves and the flow pipe still got hot 1.5m from boiler so iso valves must not be shutting off properly

 

[Billy Bob Bob]

would you agree diverter - puzled me as i turned off the htg flow and rtn iso valves and the flow pipe still got hot 1.5m from boiler so iso valves must not be shutting off properly

either diverter or more crap in the p/hex even though its new,i would try removing the existing diverter and checking that bottom assembly they do unscrew may have crud in the seating

 

[buckley plumb]

either diverter or more crap in the p/hex even though its new,i would try removing the existing diverter and checking that bottom assembly they do unscrew may have crud in the seating

will remove dv and look cheers .

 

[buckley plumb]

either diverter or more crap in the p/hex even though its new,i would try removing the existing diverter and checking that bottom assembly they do unscrew may have crud in the seating

going back this wk with diverter and taking new plate off to check it .just 100% as turned both htg iso valves off and the boiler still sits with 50 degrees on display and no hw just cool .thought it would cut out or temp rise once valves closed (chances of both passing ?) will let you know

 

[arran197]

Diverter valve. That's the old style one with the by pass pipe that runs behind the plate. If in hw mode there is leaking of heat down the flow, that's where the heat is going. With the iso valves turned off it should be better, but may be going round the bypass.

The later Duo Tecs have a different diverter valve and the bypass is deleted, it bypasses through the plate, so this problem doesn't arise. They're not interchangeable though, so you need to make sure you put the one with the bypass back in.