combi boiler question about heating

[jamesboyd]

on a combi boiler - what activates the central heating ignition sequence? is it a primary flow switch or are there various methods? I was just wondering as we have a combi and with hot water the microswitch when activated starts the ignition sequence. basically when the timer calls for heat with a combi for central heating, how does the boiler fire/ignite?

thanks for any info anyone can offer me

 

[Agile]

Different models use different methods!

I am surprised that you did not bother to tell us what model of boiler you have.

It might also help if you explained why you are asking.

Tony

 

[jamesboyd]

sorry, thanks for your reply. My boiler is a worcester Junior (28i). non condensing combi.

I was just wondering in general. I know they can vary just wondered what the most common way was.

 

[Agile]

The demand for heat either comes from the DHW flow switch or the timeclock/thermostat.

Tony

 

[jamesboyd]

thanks Agile, I appreciate your help.

I know the boiler has no diverter valve and as you say the hot water ignition happens when the flow switch operates.

In general do a lot of combi's in central heating mode start the igntition from the timeclock/stat ? Do some fire from a primary flow switch?

 

[Agile]

If they did that and the flow switch jammed then the boiler would fire when there was not flow!

Boilers are more complicated than you would like then to be.

Tony

 

[jackecole]

I disagree Agile - if the primary flow switch (for heating demand) was jammed in the on position it wouldn't make the boiler fire all the time, as there would need to be a demand ie from programmer/timer first to allow voltage (via the pcb) to activate the ignition sequence via the primary flow switch.

Also there has been times when the DHW flow switch has been stuck ON and the boiler fired constantly, and locked out soon after as draw offs all closed of course (the Puma I believe had this issue)

 

[simond]

I know the boiler has no diverter valve and as you say the hot water ignition happens when the flow switch operates.

All DIYers reading elsewhere about the Atmos/Intergas being a new idea with no diverter valve may want to read the above again. And then look up Ferroli and all the other combi boilers that also had no diverter valve.



There is (or was) a recent Baxi condenser that uses a flow switch to determine demand from the radiators, but not being a Baxi installer I can't remember which one.