Ideal Response 120 fails to ignite

[boardbabe]

I know there has been simular topics to this one and it seems the senses of opinion is the problem is the heat exchanger but when I mention this to my gas engineer he says he doesn't think so (but doesn't know what the problem is!!)
My Problem........
It is an intermitent fault that makes it all the harder to diagnose. It effects the central heating and hot water but sometimes if I flick between the two I can get it working again (but sometimes not!!).The boiler wont ignite and the burner light doesn't come on but the boiler makes all the usual noises as if its running. The burner light occasionally comes on for a few seconds and then goes out again. The pressure is fine (about 1.5bar) and doesn't drop. The boiler engineer hasn't mentioned that there is any water leakages. He has cleaned the fan and replaced the PCB and the ignition electrodes. - I still have the same problem and the engineer doesn't know what it could be.
HELP

 

[superdupergasman]

What about the dynamic gas pressure??

When it lights, if the gas pipe is undersized or the meter regulator faulty
the gas pressure will fall too low therefore the boiler will not have the correct gas/air mix thus not igniting properly.

What about a cracked burner??

Something in the flue??

Nacked gas valve??? can be checked with manometer.

 

[petit_pablo]

Spark generator need replacing. These can fail intermittantly and will just get worse over time

 

[superdupergasman]

Spark generator need replacing. These can fail intermittantly and will just get worse over time

burner light then goes out pablo!

 

[petit_pablo]

Spark generator need replacing. These can fail intermittantly and will just get worse over time

burner light then goes out pablo!

I only read half of OPs post

 

[Agile]

It seems you have a pretty inexperienced engineer.

Anyone familiar with this boiler would be checking everything and then if all seems OK replacing the cheapest and most likely component, the ignition circuit!

HOWEVER if its really lighting then its the FLAME detection electrode that needs to be checked. If the HE is leaking, when removed to inspect, the flame detection electrode comes out with a wet insulator.

Since the boiler will boil off the leaking water, an advanced technique is to light the boiler and apply a flame simulation circuit to the detection electrode to keep the burner on until it dries and the original detection electrode can be reconnected.

Tony

 

[ChrisR]

a flame simulation circuit to the detection electrode to keep the burner on

How very dare you suggest such a thing - which the owner would press to be left in place when the boiler woudn't light the next day. (Besides there's an easier way!)

For once my horse is higher than yours!

 

[boardbabe]

So... is the flame detetion electrodes different to the ignition electrodes? (I bet you can tell I know nothing about boilers!! )
I think I had the ignition circuit replaced last year so the engineer doesn't think it could be this again!!

 

[Agile]

I cannot immagine any engineer would ever use a simulation circuit for anything other than testing!

The advantage of using a flame simulation circuit is that it tests the PCB is working correctly and confirms the problem lies at the detection end.

This OP is using a gas engineer. He would be better calling you, Chris, as you are both in Surrey.

Tony

 

[boardbabe]

The engineers I'm using is through the British Gas Homecare Scheme but as you say I don't think they know what they are doing!!
If I was paying the engineer directly I would definately have gone elsewhere by now.