Vokera compact 24 problem.

[lavenders19]

I have a problem with my boiler. THe vokera engineer has been out 3 times for this fault and not fixed it. The problem is that when the boiler has been sat idle for a while (usually a few hours) it makes a bang when it ignites for the 1st time. After that it is fine. The engineer changed the gas valve on the 1st visit, changed the ignition module on the 2nd visit and increased the minimum gas pressure on the

3rd visit but no joy. I have measured the problem with a manometer and the gas valves goes to minimum pressure but no ignition. It then automatically goes to maximum pressure and ignites with a bang at the higher pressure.

When i turn off and on again it is fine, gas to minimum pressure, ignition, and then higher pressure gas.

Anyone know of any problems that the engineer is missing? Thanks in advance guys.

[Andy Hall]

Considering also your other problem, and what has been changed already, has he checked for a leak inside the boiler case?

If the pressure drop with the soundness test and this phenomenon are connected (which sounds plausible), then I'm surprised that he didn't do a test for this before.

[lavenders19]

I have isolated the gas appliances and still the problem persists

[John]

Just a thought to begin with - you have checked the integrity of the manometer and tubing before starting haven't you? Also why did you start this test - have you smelt gas?

[Ed Sirett]

If what you have been measuring was the outlet gas pressure to the burner then this is odd.

A typical sequence for the outlet gas pressure would be something like. Gas valve opens at minimum. Ignition. Flame detection. Gas goes to full rate. Ignition rate may not be the same as minimum rate on some boilers (Ferroli at least).

Having checked over the minimum and maximum gas pressures and rates. I'd then try a new PCB, whichever is connected to the modulation control on the gas valve.

HTH

[lavenders19]

I hear you Ed. I thought that it was wierd that the gas went to full rate without the flame actually lighting. This is what is causing my bang. I need to get onto Vaillant technical support to see if my boiler has a flame detection system or if it goes to full rate regardless.

[Ed Sirett]

Vaillant or Vokera?

The ignition gas rate has a marked effect on many boilers with quite small changes leading to poor ignition. It may well be that the boiler can't ignite easily at full gas rate (until the gas builds up so much that it explodes).

Some models (i dunno whether the Vokera is like this) have a separate adjustment for the ignition rate, which is independant of the minimum and maximum rates.

[John Laird]

I don't know if this helps, but the wording in the manual for my Vokera boiler tends to suggest that the "soft-light" time is quite short. I read this as meaning that the valve will open fully regardless. Ignition detect presumably follows this. There is a separate adjustment for the soft-light pressure. Maybe you could adjust this upwards slightly ?

I have had cause to call Vokera TS, and they were pretty helpful.

[lavenders19]

Just had a thought. With a slight leak in the gas pipes, now fixed by reflowing solder to all joints, would this be replaced with further gas from the meter or would the pipes fill with air. Perhaps in the past air was igniting when the gas had escaped (if not refilled imediately from the gas meter).

I say this as now the boiler is far better. No bang in the last 4 days. I did adjust the minimum gas pressure from 1.9 to 2.5 and it seems to have done the trick. I will however monitor it over the next few days.

[lavenders19]

Ummm spoke too soon, back to the bang again. Having phoned vokera technical support again, they suggest the air into the combustion chamber may need increasing by means of a baffle. Anyone know what this is and what it looks like etc. How do i adjust it to increase the airflow which they said will make ignition quicker.

Thanks