worcester 24cdi/RSF problem no light at all, please help

[alex2012]

My old worcester 24 cdi/rsf boiler broke down another day. There is no light on at all, even the green one. According to the manual it suggests a failed pcb board. I bought a new one from ebay and a new transformer as well. I managed to replace the faulty pcb and the transformer according the manual.

The boiler is in a room upstairs. There is an external switch on/off with fuse-spur of 3A to control the electro-supply in kitchecn downstairs. I trurned on the switch downstairs and the boiler upstairts. There is still no any light on however including the green one.

I checked the voltage of the switch with fuse-spur downstairs and some other parts of the pcb board with a multimeter.

Switch on/off with Fuse spur downstairs:
Brown the live to apliance: 238
Blue the neutral to appliance: 238

PCB control upstairs:
main-supply-in live:238
main-supply-in neutral: 238
Fuse one: 238
Ns&ls&Lr in ST8: all 238
ST15 to pump: L&N both 238
ST11 to flue fan: L&N both 238
Fuse 2: only 17

the pcb mode is 87483002190 which is a bit different from my orginally one which is 8748300219.

I also checked the voltage when my old pcb control was fitted on,

switch on/off with Fuse spur downstairs:
Brown the live: 238
Blue the neutral 238

PCB control upstairs:

main-supply-in live:238
main-supply-in neutral: 238
Fuse one: 238
Ns&ls&Lr in ST8: all 238
ST15 to spark electrode: L&N both 238
ST11 to fan: L&N both 238
Fuse 2: 220

However when the boiler is poited to 'turn off', surprisely there is still voltage in some parts of my old pcb control.

main-supply-in live:238
main-supply-in neutral: 238
Fuse one: 238
Ns&ls&Lr in ST8: all 220
ST15 to pump: L&N both 220
ST11 to fan: L&N both 220
Fuse 2: 140

It looks my originally pcb has faulty since even the boiler is off there is still high voltage in some parts.
How about the one I bought from ebay? is there also a faulty?

I am so confused.
Thank you very much in advance.

 

[MJN]

Hi Alex,

You don't say what you measured the voltages against, but assuming earth then your problem appears to be the lack of a supply neutral. The voltage of the neutral with respect to earth should be 0v (or thereabouts) and not 238v. With the neutral appearing at 238v, as per the live, then there's no potential difference hence no current will flow.

Start back at the FCU and measure the voltages again. Disconnecting the boiler would help pinpoint the problem.

Mathew

 

[alex2012]

Thanks for Mathew and Tom,

All the voltages are against earth (yellow&green) which is connect to the metal part of the boiler in end.
Do you mean even when the boiler is pointed to 'off' or doesn't work, the neutral volatage should still be 0? where do you think the broken could happen? between main power box and switch on/off with fuse spur or between switch on/off with fuse spur and the boier or just on the boiler?

I'll do more tests on weekend as you suggest since I am working in other city. I'll also change the fuse in the switch on/off.

Hi Alex,

You don't say what you measured the voltages against, but assuming earth then your problem appears to be the lack of a supply neutral. The voltage of the neutral with respect to earth should be 0v (or thereabouts) and not 238v. With the neutral appearing at 238v, as per the live, then there's no potential difference hence no current will flow.

Start back at the FCU and measure the voltages again. Disconnecting the boiler would help pinpoint the problem.

Mathew

240v on the Netural is showing a break in the Netural. Netural is earth return so you'd expect it to show no volts. If its broken it's got nowhere to flow to and becomes live like the live in.

 

[MJN]

Do you mean even when the boiler is pointed to 'off' or doesn't work, the neutral volatage should still be 0?

It should be pretty much zero all the time as it is anchored at, effectively, the same potential as earth.

where do you think the broken could happen?

Could be anywhere between the CU and the boiler.

Mathew

 

[alex2012]

I'll do more tests on weekend. I have some notes of my test which i did on weekend.
This is the result when I disconnected the bioler and turn off the switch on/off with fuse spur.
E: 129 (against bioler metal)
N:87 (against bioler metal)
L:87 (against bioler metal)
The voltages of L, N at the switch on/off with fuse spur seem both to be 33 (should be 129 - 87 = 42?) against the earth which is disconnect to the boiler in end but linked to the earth from main-supply, not sure I noted properly ).

I'll try to google some knowledge about wiring and electrocity. Thanks indeed.

Do you mean even when the boiler is pointed to 'off' or doesn't work, the neutral volatage should still be 0?

It should be pretty much zero all the time as it is anchored at, effectively, the same potential as earth.

where do you think the broken could happen?

Could be anywhere between the CU and the boiler.

Mathew

 

[MJN]

I'll try to google some knowledge about wiring and electrocity.

I'd get someone in if I were you. You're stabbing in the dark and I for one am not too comfortable shouting instructions to you.

Mathew

 

[alex2012]

It does make sense to find someone else who has the experience to do the job. You guys already have given me the most useful and helpful information I guess i am closing to solve the problem although i have already paid nealry £100 for the parts.
I'll come back this weekend. Thank you so much indeed. (I just wrongly clicked the ignore button and corrected the mistake

I'll try to google some knowledge about wiring and electrocity.

I'd get someone in if I were you. You're stabbing in the dark and I for one am not too comfortable shouting instructions to you.

Mathew

 

[Murf520970]

If the problems on the suppy side your better of getting a sparky to have a look, was going to comment on poss boiler problems bit re read the op post & realised its a suppyl fault

 

[MJN]

[...] i have already paid nealry £100 for the parts.

If you ultimately determine that your original PCB is actually fine then you can probably recover most of your outlay by reselling it on eBay. WB PCBs sell very easily on there, indeed there is quite a high demand for them given they are common failure points on which note it might be worth you holding on to the new one for the duration that you own the boiler as a standby spare. I can't see them ever losing value given the massive installation base.

Mathew

 

[alex2012]

I got a bit feeling the neutral breaking happened between the main-power supply and the FCU then the problem is beyond my ability to handle since the lines are hiddening in the wall. Months ago, we found at least three little mice in the house. Two were killed, one is still on the run but not seen for ages. Headache
It could also be a loose connection on the FCU which I'll check it more carefully or try to replace it.

If the problems on the suppy side your better of getting a sparky to have a look, was going to comment on poss boiler problems bit re read the op post & realised its a suppyl fault

 

[alex2012]

repeated poster. i deleted it

 

[alex2012]

Hi,
I tried to find where the neutral is broken. I disconnected the three main-power lines (one red supposed to be live, one black supposed to be neutral and the yellow/green supposed to be earth) on the FCU (the other three lines to boiler also are disconnected from FCU). I checked the voltage of these three lines from main power against the other earth which is grounded by connection to the metal panel of the boiler in the end.

Red the live against earth on boiler: 238
Black the neutral against earth on boiler: 147
yellow/green the earth from main-supply against earth on boiler: 178

Black against yellow/green the earth from main-power: 18
Black against red: 51
Red against yellow/green the earth from main-power: 36

I did some more tests. I connected both earths in FCU together and grounded it by connection to the metal panel of boiler.

Red against earth: 238
Red against black: 174
Black against earth: 37

I get confused now. Is the lines from main-power to FCU ok? Does the test suggest a short cut between the live and neutral somewhere from the air-switch box? why the voltage between the two earths isn't 0? Does it mean the earth from main-power isn't grounded?

Please help me. Thank you so much

 

[alex2012]

Hi, Mathew,

I did the test. But I get confused again. if you have a bit time, please help. Thanks so much.

Hi Alex,

You don't say what you measured the voltages against, but assuming earth then your problem appears to be the lack of a supply neutral. The voltage of the neutral with respect to earth should be 0v (or thereabouts) and not 238v. With the neutral appearing at 238v, as per the live, then there's no potential difference hence no current will flow.

Start back at the FCU and measure the voltages again. Disconnecting the boiler would help pinpoint the problem.

Mathew

 

[Murf520970]

i had a cheap test meter which read odd voltages when it should of read 0 volts . Go to the electricians forum & repost as theres a better resource of brains ( sparkys on there)

 

[alex2012]

I did post another help there. I bought the multimeter from Argos last week. It costs £29.99. I don't think i have already damaged it.

i had a cheap test meter which read odd voltages when it should of read 0 volts . Go to the electricians forum & repost as theres a better resource of brains ( sparkys on there)