Baxi bahama not heating

[tws750]

Ok here goes, hot water is working as it should, CH is dead.
Actuator moves when tap turns on, flowswitch is open circuit,shows continuity when tap turns on, water heats, all seems ok.

Move selector to dhw and ch, and the above is still true. Turn off tap and the actuator returns. Roomstat creates demand for heat, timer on constant and nothing happens. To check the CH flowswitch it is open circuit, removed actuator head, turned on tap, pump runs, flowswitch shows continuity. Radiators heat up until of course the tap is turned off.

From this, and the assumption that something must start the pump running before the CH flowswitch can work, am i looking at the pcb?
There are 3 relays on this board and again i assume one of them switches the roomstat signal to the pump.

anybody know which one? or have i missed something else?

(yes i know its a bahama, but in 8years this is the first problem i've had)

Tim

 

[Mikeyboy]

Suggest you google for baxi parts arena , and download bahama fault finding guide.

 

[tws750]

thanks, tried that. Its the same as the manual. Says a lot about HW but not much help for CH.

 

[tws750]

anyone else? any clues?

 

[ollski]

presume you have checked external controls are switching and sending voltage onwards towards the boiler?

 

[tws750]

i have, yes. Roomstat switches, live reaches pcb.
In HW mode the output terminals to the pump are live and the pump runs, but the same terminals feed the pump in CH mode and are dead.
All other terminals on the connector have a feed.
The only thing i havent done is bypass the integral timer, but power is going through it.

If it is the pcb, i'd like to prove it before shelling out for one.

 

[bones001]

i cant picture the inside of the boiler but if its anything like the genesis try swapping the connections over between the hw and ch thermistors (thats if it the same setup which if it aint ignore this!)

 

[ollski]

ok, measure across white wire on 3 and neutral on the main terminal block with everything calling and power on.....what we got (acv)?.

While you're at it disconnect the dhw flow switch next to the pump and try the heating then.....I know you've checked them but just to be sure as it is almost always the problem.

 

[tws750]

ok, main neutral and white wire on CN3 (its a SIT board) shows 240V.

DHW flow switch disconnected makes no difference.

I havent tried the thermistors

 

[tws750]

sorry, its on CN2 not 3

 

[ollski]

white wire on 3 is 8 up from the bottom, if you have 240 then try terminal 4 (9 from bottom) to neutral. If you have 240 there then suspect the pcb, but you may also want to clean the ch filter.

pump is first port of call by the way after flow switches and demand for heat

 

[tws750]

white wire on cn3 (valve modulation) terminals 1+2 shows zero volts
white wire on CN2 (roomstat input) terminal 1 shows 240v
not sure which you mean by terminal 4 so ive checked them all for 240v to main neutral
CN3 none
CN2 term 1 white roomstat input 240v
term 2 orange from neon 240v
CN1 term 2 brown to diverter valve 240v

 

[ollski]

we are on the terminal block here, not the board.

 

[tws750]

ah, ok ..... i'll go look

 

[tws750]

right, i have 240v at both white wires and both roomstat terminals

from this i assume the demand for heat is proved to exist, and the white continues to the pcb, which turns the pump on, so the flowswitch can tell the actuator to move and the ignition to fire. Or in my case it seems it doesnt.

i'm also assuming that as i can heat the rads by removing the actuator and running a tap, that the CH filter must be clear.