Baxi 100 HE condensate trap causing flame failure

[TheGasEngineer]

How to test a Baxi condensate trap.

This condensate trap is used in a number of Potterton boilers as well so I understand and it can be the cause of a flame failure lockout.

Baxi will tell you to disconnect the white wire by the fan and if the boiler runs it's a damp trap....

Well it would be damp. It's a trap! So I asked how I test the trap resistance to see if it's ok? They didn't know. I asked what resistance would trigger flame failure? They didn't know... Hmmm

So I put a 250v insulation resistance test between the trap white wire and the case (and it must be disconnected from the PCB please!!) and got 7MegOhms.

Now 7MegOhms is a high figure but nevertheless this triggers flame failure. A quick clean and another reading showed >200MegOhm and this time the boiler ran. The problem is I don't know what the critical resistance is - the value where the boiler will *just* run but lets say it's 100MegOhm

The point is, during a service do the test and if the reading is 100MegOhm then it's clean enough. If it's less, dry the terminals and re-test. otherwise next week it might go critical and you get a call-back...

If the boiler suffers flame failure and the resistance is >100MegOhm then the PCB is probably US. Without this measurement there is no way of being absolutely sure which part is the problem.

 

[Toddyplumb]

But if its getting damp/wet in the top pocket of the trap something is wrong somewhere . Are you having a lot failing on this ? As you know it is to detect condensate line blockage

 

[TheGasEngineer]

I've only had a couple of instances but the problem was more that Baxi do not have a test procedure which is nutty.

The top of the traps in question were slightly dusty / greasy / damp. And the trouble with working at these levels of resistance is the slightest bit of finger grease can make a massive difference. The PCB triggers in the rhelms of megohms which is just not necessary. Its an inappropriate design. But as that's the design we are stuck with, it's essential to have a means of finding the problem without having to guess.

If the PCB triggered at a lower level of resistance, the only time it would trigger is when the trap was full which is the whole idea of the design. In that case, the muck on the top of the trap would be much less of a problem.

 

[Billy Bob Bob]

i think the answer to all your baxi 100 he problems are simple,condem them all and put them in the bin as they all sheds,as to trap issues its bloody easy pull the white wire off it will be in continuity with the ignition leads/ pcb if the traps full if its off to lockout and it runs the traps blocked/condensate frozen and to throw a spanner in the works performas/105he had a problem where the screw holding said white wire to trap was to long causing this sort of problem and your wrong a trap will only be wet one side thats the idea if the other side fills up you have a problem bingo your lockout fault

 

[diesel_ltd]

if you cut the white wire and your sump on the heat exchanger gets blocked youll not know a thing about it till its too late i have seen this lots of times, never cut the wire.........

 

[Toddyplumb]

You dont cut the wire , there is a spade connector you simply disconnect to test