britony flexiflue pcb fault

[nrgserv]

responses appreciated for the following problem-

according to the schematic for the flexiflue in the installation manaul (WHICH APPEARS TO BE WRONG!), relay 1 holds the pilot light on through the thermocouple and theroelectric valve and relay 2 (puled in) when no pressure drop is sensed. when water is drawn, relay 2 should drop out and the pressure switch should change contacts holding relay 1 in.
the problem i'm having, is the pilot wont stay lit when water isnt being drawn due to relay 2 not pulling in. the fan speed will change to high, the pressure switch activates, but according to the drawing (WHICH IS STILL WRONG....) i'm not getting the 130v across relay 2 that i need to pull it in.

has anyone had this problem before, or has anyone got a CORRECT schematic diagram to assist in correct fault finding!

incidentally, if hot water is drawn, relay 1 pulls in (due to the pressure switch changing contacts and relay 2 is already in its de-energised state) and the pilot light can be lit and the water heats up. soon as the taps shut off, water flow swich closes, shuts fan to slow, pressure switch changes, relay 2 dont do owt, so relay 1 drops out and pilot goes out.

technical talking point if nowt else, tho its damned annoying.

cheers,

nrg

 

[Agile]

I think that Chris R has noticed this problem a couple of years ago.

If he does not reply soon send him an email and ask him to reply here as it has general interest to boiler engineers.

Tony

 

[nrgserv]

cheers agile, currently browsing the rest of this forum to find out how it works. (minor differences to the others i use!)

neil

 

[nrgserv]

I think that Chris R has noticed this problem a couple of years ago.

If he does not reply soon send him an email and ask him to reply here as it has general interest to boiler engineers.

Tony

not sure on the definition of soon, but done it anyway!
cheers

 

[Agile]

A simple search found it! Amazing what rubbish I seem to remember!

Chris said this in January 2007 ( a "couple" of years ago to within a few days! ) :-

1st visit Weds "Not lighting properly" so I took a diaphragm. The black plastic disc the diaph pushes was broken up. Didn't have one of those.
Bought service kit

2nd visit, Thurs changed that, and the thermocouple. The tc solenoid was dud. Have never changed one of those, didn't have one.
Bought solenoid.

3rd visit, Fri before Xmas changed that, and piezo ignition & electrode cos it wouldn't light pilot properly, and it ran fine for a week.

Then (Today, 2nd Jan)No hot water. Report first came that the fan was running (slowly), so the gas valve must be sticking to break the plastic disc, according to chaff.
Searched country, found only 2, miles away. Gloom.
Wondered if punter was turning the knob to "run" so rechecked ... and
Report came that it was dead, and fan not running. So, knowing the APS can blow fuses on those, I bought one. (About £100 retail!)
This takes time!!

4th visit Put fuse in, fan ran, but lotsa sparks.
Parts on pcb blown to bits.

Took APS back to supplier for credit.

5th visit, took a "New" unused pcb I've had for a while - it was my father-in law's...
It worked a bit, then it didn't.
Spent an hour with a soldering iron trying to get one board working from the old and the new, but the circuit diagram in the manual is WRONG and there seemed to be more than one fault on the unused pcb. Late, gave up, went home.
6th visit, took a new new pcb.

Are you still sure that you want to fix yours?

Tony

 

[ChrisR]

I'd actually forgotten that until Tony dug up the old post. Yes the pcb didn't match the cct diagram.
Caps drying up often make the board fail as the overlap times get short. Board also fails if (as sounds the case in your boiler) the resistance of the relay contacts is above a fraction of an ohm. Thermocouples work with of the order of 10mA and 10mV, so with one ohm you lose all your voltage across the relay contact instead of the solenoid.
Prove it by measuring mV DC across the contacts on the pcb.

 

[nrgserv]

I'd actually forgotten that until Tony dug up the old post. Yes the pcb didn't match the cct diagram.
Caps drying up often make the board fail as the overlap times get short. Board also fails if (as sounds the case in your boiler) the resistance of the relay contacts is above a fraction of an ohm. Thermocouples work with of the order of 10mA and 10mV, so with one ohm you lose all your voltage across the relay contact instead of the solenoid.
Prove it by measuring mV DC across the contacts on the pcb.

been there!
thermocouple, r1 contacts, thermoelectric valve all good.
20mV at t.c., 14mV at t.e.v. (more than 12mV required for t.e.v.)

it all actually works fine when on high fan and drawn water. it also works fine when you dig a hole in the top of r2 and over ride the contacts. just cant work out what holds r2 in, partly due to the diagram being wrong. (thats when we found the descrepency!)

its not my boiler (fortunately, a mates) and we've found a new pcb on ebay for a tenner (so far) so he stuck a bid on it. we also have a 125vdc relay on back order from RS (ordered on monday) which will get changed to see what happens.

if we win the pcb, gonna produce a new diagram from the old one so to see the differance. will post the findings.

meanwhile........ if anyone already has a correct drawing, or more experience of this cak bit of electronics, feel free to post!

ta all,
neil

 

[Agile]

Dont expect anyone else will have a diagram!

The manufacturer's dont release them ( or even have them in many cases ).

There are only about five engineers who would be able to or bother to trace it, one of them is me and another is Chris!

If you traced it out then I should be able to tell you what is likely to be wrong.

Tony

 

[waterworks]

Sorry to hijack this thread but i went to one of these today which had blown the onboard fuse, when i removed the board it was badly burnt and the relays looked quite burnt.

I have ordered a new pcb which i'm picking up tomorrow, but i'm a bit worried about your statement (So, knowing the APS can blow fuses on those, I bought one) could you explain what you mean please before i fit the new board.