Worcester 28CDi Hot Water works, but Central Heating doesn't

[jasonfrog]

Hello one and all. My first post.... and no surprise I'm looking for some help.

I've got a Worcester 28CDi RSF Combi Boiler

It provides hot water without a problem. However Central Heating isn't working.

When I switch the CH on, the fan clicks on and spins up and then immediately clicks off and shuts down. 20 secs later the Hot Water light starts flashing fast, indicating an 'Air Pressure Fault'.

It doesn't get as far as firing up.

Any ideas? I can provide more information as required.

 

[clf-gas]

Air pressure switch, APS, sounds like it aint closing to make circuit.

 

[alan m 1974]

aps? but h/water ok,so i think aps ok

 

[jasonfrog]

Air pressure switch, APS, sounds like it aint closing to make circuit.

like alan above says, I thought that it won't be the APS as the boiler fires up and provides hot water/DHW.

(edit: Many thanks for the quick responses )

 

[alan m 1974]

see the c/h sensor can you check it or arent you used to a m.meter

 

[alan m 1974]

It does seem like a pcb,but thats the final thing

 

[jasonfrog]

see the c/h sensor can you check it or arent you used to a m.meter

i've located the c/h sensor (to the left of the combustion chamber, yeh?) and i've got a multi-meter .. how should i check it?

 

[alan m 1974]

SEE the h/water sensor take it off and try the c/h sensor leads on it just swap them over

 

[alan m 1974]

Then you will know if its working if the h/water works when sensors are swapped over,thjats a 100%way,isnt it ,that will narrow the proplem down

 

[jasonfrog]

SEE the h/water sensor take it off and try the c/h sensor leads on it just swap them over

ok, just tried doing that. i disconnected the leads from c/h sensor and the h/w sensor and then attempted to swap them over. unfortunately they are not long enough and don't reach. so i reconnected them as they were and closed everything back up.

i tried the c/h again... and it came on!.... but after about 1 minute I heard the fan switch off, and then soon after the 'Air Pressure Fault' light flashing started and the burner cut out.

so switched everything off and then back on again and gave it another go and it's back to the fault described in my first post.

i guess to try and do the lead, swap as you suggested, i will need to make up some extension leads just for the test?

many thanks for your help.

 

[alan m 1974]

NO ,TAKE THE SENSOR OFF THE H/W PIPE AND JUST PUT IT ON THE C/H LEADS,ITS THE SCREW TYPE ON THE H/W ISNT IT

 

[alan m 1974]

Jason,just look at the h/w sensor undo screw,take the clip off and just put it onto the c/h leads and h/w leads onto the c/h sensor which just pulls off

 

[jasonfrog]

Jason,just look at the h/w sensor undo screw,take the clip off and just put it onto the c/h leads and h/w leads onto the c/h sensor which just pulls off

hah, sorry for my misunderstanding. ok yeh i got you now. yes, the h/w sensor is mounted on a screw clip and the c/h sensor is on a spring clip.
i've removed them both and have swapped the leads.

should i remount them now?

(i.e. take the h/w sensor out of the screw clip and put it in the spring clip, and vice versa for the c/h sensor?)

 

[alan m 1974]

yes try it with them both connected to the sensors but just swapped them over,if the heating is ok then you know its a sensors if its not then sensors ok and now we go to a step closer to pcb,i would also check the harness going into pcb,it has a harness that has loads of wires on it going to the pcb but it can come loose,it is on your right as you lower the facia,no undo the 3 screws on the front so the bottom bit comes away and you will se it ,right hand side white harness,3000000000000 wires just make sure its all the way in and check the timer,built in? white grey,brown any roomstat?if not cable is in from rs to rl,

 

[jasonfrog]

yes try it with them both connected to the sensors but just swapped them over,if the heating is ok then you know its a sensors if its not then sensors ok and now we go to a step closer to pcb,i would also check the harness going into pcb,it has a harness that has loads of wires on it going to the pcb but it can come loose,it is on your right as you lower the facia,no undo the 3 screws on the front so the bottom bit comes away and you will se it ,right hand side white harness,3000000000000 wires just make sure its all the way in and check the timer,built in? white grey,brown any roomstat?if not cable is in from rs to rl,

Made the swap, same problem, so it's not the sensors. Checked the harness and it's definitely seated in tight. I don't have a room stat, which means I do have a link between Ls and Lr.. which seems to be in place ok. I've got a digital timer, which seems to work ok. I removed it anyway so that CH would come straight on (if it was working). Still the same issue.

Anything else left to check before I seek out a replacement PCB?

(Just a had a quite look on ebay and there is someone that does warrantied replacement PCBs for £55 in exchange for the faulty one)

Huge huge thanks for all your great advice and help. Really appreciate the time and thought you've taken.