How hot water works on a combi boiler

[StuartTaylor]

Hi everyone

Can someone help me, or correct me please.

I'm trying to work out how combi's work, I know they are hot water instantaneous and have no stored water like a cylinder system does

But do they operate in different ways for hot water.


Is this how they work when a hot tap is opened:

Water passes through diverter valve, diaphragm deflects upwards, pushes microswitch up to close switch and send power back to pcb

pcb then (if hot water thermistor calling - working ok) sends power to fan/aps/gas valve/ignition etc?

Or does the microswitch from the diverter send power to the pump, which then activates the main flow switch when in turn, if hot water thermistor working / calling - activates ignition (fan, aps, gas valve, etc)

 

[ianniann]

It varies.

 

[StuartTaylor]

Do you mean depending on the combi make/model? I know some have flow switches instead, and no diverter valve or some have a flow switch and a diverter valve.

 

[Mr Smyth]

Probably most but not all combi's use a diaphragm to detect the hot tap turning on.

With modern combi boilers pretty much everything is controlled by the PCB

 

[StuartTaylor]

What would the signs be or likely faults be with a combi if you have no hot water at taps and it's just running through cold?

 

[Mr Smyth]

Boiler make and model would help.

Does the boiler fire for Htg? This pretty much tells you if the boiler simply works or not.

If this has a diaphragm does the pin move? to operate the microswitch?

 

[sooey]

The gas has ran out.

 

[StuartTaylor]

I don't have a fault I was just enquiring about combi boilers as I am moving into a flat with one and have heard they can go faulty quite often! Was just trying to find out about them from anyone who could help.

 

[Mr Smyth]

Tell us the Make and model and we can advise you on rough age, regular faults etc.

But don't worry yourself into a fault

 

[StuartTaylor]

Ok thanks for your help

It's a worcester junior 28i

 

[Boilerman2]

My Combi is three years old, it hasn't gone wrong yet (touch wood!)

 

[Agile]

My Combi is three years old, it hasn't gone wrong yet (touch wood!)

Yes, but its not a Worcester 28i !

They are not one of the most reliable boilers!

Tony

 

[Mr Smyth]

Yes, but its not a Worcester 28i !

They are not one of the most reliable boilers!



It may not be ideal...... but at least its not an Ideal