boiler won`t switch off.

[Agile]

no demand from external stat,
with primary flow switch disconnected(red wires) boiler does not light, although pump runs and primary spindle operates switch, no dhw either.
with p/flow switch connected and plunger held down manually, dhw works,
i.e. turn on tap and boiler lights.

I expect that you have misquoted that.

Are you suggesting that it works properly if you manually hold down the pin?

How many contacts has the microswitch?

If only two then there is no possibility of a mis connection.

If three then it could have been connected tot he wrong terminals.

However, I expect this is a red herring and you have said something you did not mean.

Tony

 

[malc19591]

thanks Dave,
will give that a go when I get in tonight, I notice there is an ignition pcb fitted.
might be worth investigating that.if its a separate unit which appears to be on the wiring diagram.
thanks
malc

 

[malc19591]

hi Tony,
yes if i hold down primary pin manually, dhw works as it should i.e. lights and extinguishes boiler by turning taps on and off.
but obviously no ch. as soon as pin released burner lights and stays alight.

 

[Agile]

That seems very unusual!

I assume its only a two connection microswitch with no possibility of misconnection.

Although the Alpha PCB is very reliable, it really does sound as if its a PCB fault.

UNLESS ???

Have the wires to the DHW flow switch and the primary flow switch been crossed over?

Regardless of what you think try changing them over!

Tony

 

[malc19591]

both micro switches are 3 connection.
tried swapping as suggested and the result was.;
boiler did not light when power switched on although primary pin operated switch.
no ch when external stat asked for heat.
dhw worked as should .
is it possible some idiot (me) has got micro switch connections wrong?

 

[Agile]

The last Alpha 240 I saw a few days ago only had two wires on the DHW switch! I think they were both red but might not have remembered that correctly.

I think its very likely the wires have not been correctly connected.

As the DHW now works correctly then that might be the correct connection.

The service manual should give adequate information to indicate where the wiring should be connected.

Tony

 

[gas4you]

The DHW switch (front switch) should have the green wires to it, whilst the primary flow switch (top switch) has the red wires to it.

 

[malc19591]

before i altered them the 2 red wires were on the primary, the 2 green on dhw.
the switches have three connections.
will check wiring diagram later, off to work now.
thanks for help fellas will let you know outcome tomorrow.
malc

 

[gas4you]

Perhaps you have the wires connected to the wrong terminals then. Should be connected to 1 & 3 on both.

 

[Agile]

Not all microswitches necessarily have the same numbers.

I would say they should be on the Common (C) and the Normally Open (NO).

I would also only expect TWO wires to each switch but the OP implied he has three ??

The boiler I went to recently only had two tags on each switch. Of course the standard microswitch has three. One can never assume anything one finds on a boiler is the original and the manufacturers have a habit of minor changes to parts like this from time to time.

Oddly the Baxi/Potty versions usually have three wires connected to the DHW switch. Thats why the OP could also have three on his too.

Tony

 

[matt1e]

Confusing one.

Try 'wiggling' the knob on the gas valve that you press to light the pilot. There is a micoswitch on this that activates the fan and spark etc. The fan should come on at full speed to start with, then when pilot is established, slow to tick over.

Could be this is stuck in the on position.

Otherwise starting to look more like the pcb.

We need Paul Barker to pick up on this post. He's the Alpha expert on here

very confusing but I would definitely start here
if the microswich is stuck on (which I think is) the ignition sequence will continue sparking and the fan will be continuously held at full speed but now the gas valve is free to fire (thermocouple proved ) It could be that the main PCB is now "confused"
I would do as gas4you has suggested if "wiggling the gas knob" has no effect disconnect the ignition switch from the ignition pcb by removing plug M1 (with the pilot on) if the switch is stuck removing the plug will stop the sparking and the fan should go to slow speed

now check the boilers operation

 

[malc19591]

yes thanks for that,
quick update.
3 pins on both switches, only 2 wires, 1 and 3 connected, red on primary green on dhw.
wiggling had no effect
disconnected ignition wire at pcb( ignition)
now when powered up the following symptoms;
boiler lights immediately.
no clicking from ignition module ( switch stuck as suggested)
for some reason able to control ch from dhw stat on front of boiler i.e. turn stat to approx 1/4 and boiler cycles on and off.
ch stat has no effect.
going for pcb.
all hope is lost.
any ideas.

 

[matt1e]

disconnected ignition wire at pcb( ignition)

was this the blue and brown from M1 you disconnected or the black wire from the transformer (it should have been blue and brown)

also the pcb has a built in frost stat that could be operating

from the manual

The boiler incorporates a built in frost thermostat which automatically turns on the boiler and pump if the water in the boiler falls
below 5°C, providing the electrical supply neon is illuminated and, if applicable, the pilot is alight. The boiler will operate until
the water temperature in the system reaches approximately 30°C

if not its begining to look like a new pcb (and ignition switch)

 

[Agile]

yes thanks for that,
quick update.

for some reason able to control ch from dhw stat on front of boiler i.e.

all hope is lost.
any ideas.

You should easily be able to realise that the boiler is in the DHW mode!

Either the DHW demand switch is faulty or more likely you have fitted the two wires on the wrong contacts. They should be on "C" and "NO" !

Or just take them off and the DHW demand should cease!

Compared with an A380 Airbus that boiler is a pretty simple piece of kit!

Tony

 

[malc19591]

blue and brown wires disconnected from ignition pcb.
green wires on dhw switch on "c" and "no".
with green wires disconnected boiler still operates.
only thing that turns boiler off if dhw stat turned to approx 1/4 or less or red wire removed from primary switch.