Soft ignition

[JonathanM]

In researching a new boiler, I've come across quite a few references to "soft ignition".

How does this work, and is it beneficial?

 

[DP]

Burner is ignited at minimal air gas mix, upon ignition the mix is ramped up slowly instead of to max burner pressure

 

[JonathanM]

Burner is ignited at minimal air gas mix, upon ignition the mix is ramped up slowly instead of to max burner pressure

Thanks. Is this on all boilers, these days? When I've checked back, most of the references to it are for Vokera and Ariston boilers.

Also, a Worcester boiler refers to ignition sequence, followed by a "102 second soft start". Is that the same thing?

 

[Johntheo5]

It would be great if they all had a soft start as there would then be little or no flow temperature overun and the boiler could then cycle quite happily without resorting to measures like extended anticycle times to get the boiler temperature low enough to avoid SP+5C on fire up with 65% or so ignition settings, even worse some like vaillant keep (or used to) these settings for 60secs before modulation, no doubt they have very good reasons for doing so , emissions??.

 

[JonathanM]

It would be great if they all had a soft start as there would then be little or no flow temperature overun and the boiler could then cycle quite happily without resorting to measures like extended anticycle times to get the boiler temperature low enough to avoid SP+5C on fire up with 65% or so ignition settings, even worse some like vaillant keep (or used to) these settings for 60secs before modulation, no doubt they have very good reasons for doing so , emissions??.

I saw an interesting setting on an Alpha boiler the other day. You can set it so that, for the first 60 seconds, it ignores a flow temperature of up to 15C above the normal SP+5 cut off.

 

[ianmcd]

Burner is ignited at minimal air gas mix, upon ignition the mix is ramped up slowly instead of to max burner pressure

Not strictly true my friend, on some boilers the ignition burner pressure is higher than the gas valve min pressure, Vokera Excell E is a typical example

 

[DP]

Not strictly true my friend, on some boilers the ignition burner pressure is higher than the gas valve min pressure, Vokera Excell E is a typical example

I said minimal Ian, not minimum

 

[ianmcd]

I said minimal Ian, not minimum

still not correct mate whether minimal or minimum, the ign settings are what they are for different boilers

 

[DP]

still not correct mate whether minimal or minimum, the ign settings are what they are for different boilers

Ian the question asked is “what is soft light”, not what is modulation minimum or ignition pressure setting, which you are correct need not be the same. Furthermore will the Excel 80e even ignite at minimum burner pressure reliably hence the ignition sequence burner setting is higher?

The answer ( in my mind) is the gas valve ramps up from ignition of burner to max rate smoothly instead of low modulation setting to max burn

Ignition setting has nothing to do with soft light ( which is function of the gas valve, not pressure setting value which is determined to reliably ignite the burner without a thump). only connection is burner lights and then smoothly rises to max value.

I fail to see the connection between low burn pressure ( which will only be effected when operating temperature is reached) and the ignition pressure setting for the burner at which it ignited from which the gas valve ramps up.

 

[JonathanM]

Ian the question asked is “what is soft light”, not what is modulation minimum or ignition pressure setting, which you are correct need not be the same. Furthermore will the Excel 80e even ignite at minimum burner pressure reliably hence the ignition sequence burner setting is higher?

The answer ( in my mind) is the gas valve ramps up from ignition of burner to max rate smoothly instead of low modulation setting to max burn

Ignition setting has nothing to do with soft light ( which is function of the gas valve, not pressure setting value which is determined to reliably ignite the burner without a thump). only connection is burner lights and then smoothly rises to max value.

I fail to see the connection between low burn pressure ( which will only be effected when operating temperature is reached) and the ignition pressure setting for the burner at which it ignited from which the gas valve ramps up.

I've been looking at another boiler today, where it ignites at 2800 rpm by default, and then you can choose how long it takes to ramp to maximum. Anywhere from 0 to 14 minutes. Is the ramping up, from ignition to max, the "soft" part of the process? If so, it sounds like "soft" is actually nothing to do with the ignition itself? On this boiler, the ignition can actually be varied from 1500 to 4000 rpm, which I didn't think was something you could usually change. I was also wondering why the minimum output isn't set to lowest fan speed. I thought the lowest modulation possible would be desirable.

 

[DP]

I've been looking at a boiler today where it ignites at 2800 rpm by default, and then you can choose how long it takes to ramp to maximum. Anywhere from 0 to 14 minutes. Is the ramping up, from ignition to max, the "soft" part of the process? If so, it sounds like "soft" is actually nothing to do with the ignition itself? On this boiler, the ignition can actually be varied from 1500 to 4000 rpm.

Afraid now you are dealing with different type of gas valve

LEL, air to gas mix is 5%

Any ”lower” ( I say lower which my or may not lead to ignition of the mix*)

The fan is run at low speed ( gas valve regulator set) to provide stable flame on the burner when ignition sequence is initiated, resulting in makers specified CO2 in the exhaust. After ignition, the fan starts to pull gas from the gas valve as it speeds up. At max speed the manufacturer provided CO2 figure is set on the gas valve.
To reach max setting is now a software programme rather than internal working of a gas valve**

*case in point. At times the pilot injector may block up partially. Spark at the pilot burner may not ignite the gas mix but a naked flame might.

** Honeywell V4600A1023 is fast light gas valve. Honeywell V4600c1029 is soft light gas valve. Both gas valves are identical to look at. It is the internal function that leads to slow rise of gas pressure to the burner

 

[JonathanM]

Afraid now you are dealing with different type of gas valve

LEL, air to gas mix is 5%

Any ”lower” ( I say lower which my or may not lead to ignition of the mix*)

The fan is run at low speed ( gas valve regulator set) to provide stable flame on the burner when ignition sequence is initiated, resulting in makers specified CO2 in the exhaust. After ignition, the fan starts to pull gas from the gas valve as it speeds up. At max speed the manufacturer provided CO2 figure is set on the gas valve.
To reach max setting is now a software programme rather than internal working of a gas valve**

*case in point. At times the pilot injector may block up partially. Spark at the pilot burner may not ignite the gas mix but a naked flame might.

** Honeywell V4600A1023 is fast light gas valve. Honeywell V4600c1029 is soft light gas valve. Both gas valves are identical to look at. It is the internal function that leads to slow rise of gas pressure to the burner

Such great info. Thanks. I had no idea there were different types of gas valve. I'm hoping I'm getting the hang of it now a bit. So, does this boiler have a fast light valve - and all the ramping up is controlled by the fan through the software? Whereas proper soft light is through a special type of gas valve?

I think I may have edited my above post whilst you were replying. Did you see the table above and my query about modulation?

 

[DP]

Such great info. Thanks. I had no idea there were different types of gas valve. I'm hoping I'm getting the hang of it now a bit. So, does this boiler have a fast light valve - and all the ramping up is controlled by the fan through the software? Whereas proper soft light is through a special type of gas valve?

I think I may have edited my above post whilst you were replying. Did you see the table above and my query about modulation?

Fast light and soft light valves were used for standard efficiency boiler only ( I could br wrong there).
What you mentioned about fan rpm, will be using a zero governor gas valve. Different beast entirely.

 

[JonathanM]

Fast light and soft light valves were used for standard efficiency boiler only ( I could br wrong there).
What you mentioned about fan rpm, will be using a zero governor gas valve. Different beast entirely.

Thanks. Great video. It's a steep learning curve!