Baxi combi instant 80 he , no hot water

[flesi]

Working on Baxi combi instant 80 he, it works on heating but not hot water. New diverter valve and new plate heat exchanger installed by another engineer still no hot water. Can anyone shed any light?

 

[diamondgas]

Hot water flow switch sticking or diaphragm split perhaps or the microswitch faulty? Have you checked to see if the switch is being made and if so you need to check for continuity through the switch .. 1st thoughts...

 

[flesi]

Cheers Diamondgas for reply, the boiler even fires up on hot water demand for few seconds but still no hot water.

 

[diamondgas]

Any lights flashing? Does it fire up then go cold, burner off? If so then still looking at water flow switch. If a diaphragm is pinholed it can work briefly until the pressures equalize through the hole!

 

[flesi]

No flashing lights, it does fire up then burner goes off after 5seconds . It's new diverter valve fitted on it, u can see the pin moves when is hot water demand.

 

[diamondgas]

does the hot water demand light come on and stay on when a hot tap is opened? Turn the hot water control pre-heat stat to off when you test the hot water... see what happens If the switch is making then that light should stay on perminent not flashing

 

[diamondgas]

The domestic hot water switch is separate from the diverter, by-the-way...? The switch on the diverter is the pump flow switch

 

[flesi]

The hot water demand light stays on when hot tap is opened and preheat is off

 

[diamondgas]

I've got to go flesi ... sounds like you've proven that a demand for hot water is definitely being made.... so when there's no burner lit is the pump and fan running? If not check for continuity through the pump flow switch and aps? Without seeing what's happening it's hard to be exact mate .... Good luck and I'll catch up later see how you're getting on

 

[Billy Bob Bob]

as steve said either small dhw diaphragm split or valve snapped or ntc fault

 

[flesi]

as steve said either small dhw diaphragm split or valve snapped or ntc fault

Cheers gas man, the issue in the first place was no heating but hot water was ok. So the previous engineer has changed the diverter valve then heating was ok but not hot water. I did change the small dhw diaphragm still no hot water. I'll try the ntc tomorrow and see what happens but still I'm not convinced .

 

[buckley plumb]

link out the micro switch to eliminate that

 

[Ermintrude]

If u short out two green wires on microswitch does demand stay on ? If demand is constant sensor issue. Did pcb get a wash at all?

 

[Ermintrude]

link out the micro switch to eliminate that

My thoughts the same but stopped to pick up stuff and you already posted! Well a duplicate and then and explanation post is useful in that it's an extra two posts!!

 

[zeebeedee]

Always a nightmare following someone else's mistake!

 

[buckley plumb]

If u short out two green wires on microswitch does demand stay on ? If demand is constant sensor issue. Did pcb get a wash at all?

I washed one once by mistake - covered the control with a cloth and a bin liner over that and taped up and it still got wet water run down the wires into the board - didn't notice and turned it on that cost me

 

[diamondgas]

flesi, If the demand light's staying on and no burner then you got to know whether the pump is running and being proven, fan is on and being proven, if they're ok then you got to check out the hot water thermister, swapping its probably the easiest to do

Are you getting a flow through the plate hex? Does the boiler 'dump down' the heating flow?

Is the diverter actuator working?

You can put the boiler into heating mode, turn off preheat and demand heating, take the actuator off and manually move the spindle to see of the water flow is being diverted .. watch the burner/feel the heating flow and return to main hex above pump to see if you're getting a flow through the phex ..

 

[buckley plumb]

flesi, If the demand light's staying on and no burner then you got to know whether the pump is running and being proven, fan is on and being proven, if they're ok then you got to check out the hot water thermister, swapping its probably the easiest to do

Are you getting a flow through the plate hex? Does the boiler 'dump down' the heating flow?

Is the diverter actuator working?

You can put the boiler into heating mode, turn off preheat and demand heating, take the actuator off and manually move the spindle to see of the water flow is being diverted .. watch the burner/feel the heating flow and return to main hex above pump to see if you're getting a flow through the phex ..

steve do you know if the voltages on the diverter stay or not - went to baxi last wk on duotec hea and they said when call for htg diverter head powers for 15 sec to htg position then locks in and looses 240v when hw trhen the same powers to hw for 15 sec then locks in that position then 240v goes is it the same with the 105

 

[flesi]

flesi, If the demand light's staying on and no burner then you got to know whether the pump is running and being proven, fan is on and being proven, if they're ok then you got to check out the hot water thermister, swapping its probably the easiest to do

Are you getting a flow through the plate hex? Does the boiler 'dump down' the heating flow?

Is the diverter actuator working?

You can put the boiler into heating mode, turn off preheat and demand heating, take the actuator off and manually move the spindle to see of the water flow is being diverted .. watch the burner/feel the heating flow and return to main hex above pump to see if you're getting a flow through the phex ..

Demand for hot water stays on and the burner comes on for few secs , pump & fan run, getting flow through plate hex. Pulled out the diverter actuator , u can see the pin moving when is heating demand. I'll check the thermistor tomorrow . Thx for your help.

 

[lame plumber]

probably the thermistor in the first place all along. keep one in the van fm now on

 

[JamesyGoosey1]

I had exact same fault and it was the thermistor pal!

 

[Billy Bob Bob]

thermistors easy to test if it aint got 11k cold or the readings bouncing or says 0 its foobared

 

[diamondgas]

Once followed a guy who'd replaced the PCB and got the knob spindles in wrong .. hot water was a bit dodge then too

 

[Ermintrude]

I washed one once by mistake - covered the control with a cloth and a bin liner over that and taped up and it still got wet water run down the wires into the board - didn't notice and turned it on that cost me

Washed loads of them normally when doing diaphragm and the expansion is full of water and air lock moves! I just dab it dry and 3 mins with a hair dryer works a treat!!

 

[Billy Bob Bob]

Washed loads of them normally when doing diaphragm and the expansion is full of water and air lock moves! I just dab it dry and 3 mins with a hair dryer works a treat!!

i always remove the pcb Honeywell dry out nicely and survive Siemens dont the instants used both