Ideal Mini C28 hot water mystery problem

[Toxtoth]

Hi all,
I'd be grateful if someone could advise on the possible causes of a boiler problem I've been having recently. It's got me stumped!

Model: Ideal Mini C28 combi (the older standard model, not the HE model)

The CH work perfectly fine, but the burners do not ignite if just hot water is being called (i.e. If the burners are already lit because CH is being called, then the burners stay lit and hot water works fine).

The demand is DHW is recognised by the boiler but it locks out after 5secs or so
So far I've checked the following:

• Water pressure looks good at around 1.5 bar
• Gas pressure looked good at 11mbar
• The boiler correctly registers the demand for DHW (red LED on the microswitch shows correctly).
• The divertor actuator seems fine and is getting right voltage from PCB
• The divertor pin doesn't seem to be stuck
• When the burner is lit, the gas modultes correctly when turning the heat dial up and down

From the service manual, the diagnostic lights indicate "Faulty primary circuit (no water or absence of flow)"

However, I can't see how this can be the case as the hot water flows fine if the boiler is already lit from CH demand.

Any ideas!?! exactly what would trigger that diagnostic message??

any help much appreciated!
Toxtoth

 

[Puddle]

Would say maybe plate heat exchanger blocked not allowing enough flow round boiler to activate flow switch

 

[Toxtoth]

Would say maybe plate heat exchanger blocked not allowing enough flow round boiler to activate flow switch

Indeed; that's what I though but it doesn't make sense to me that if the CH is already on then the hot water flow rate seems fine and the boiler doesn't lock out? would this still be explained by having clogged up secondary heat exchanger?

 

[Puddle]

Maybe when heating on and hot water turned on,flow switch is already up and activated and on the hot water mode enough flow rate to keep operative however when hot water activated by its self with heating off ,ie boiler off ,flow switch has to operate from fully closed position and flow rate maybe not enough to activate from this position

if you watch you may see the pin on micro switch drop slightly put still activate micro switch when turned over from heating to hot water

 

[William Reyes]

Puddle, sorry for my ignorance but what do you mean by

(if you watch you may see the pin on micro switch drop slightly put still activate micro switch when turned over from heating to hot water)???

Am having the same problem as toxtoth but in a Ideal Mini c24 and am thinking just cleaning the HE, what you recon?

Thanks

 

[Toxtoth]

In the service manual it is called "CH Flow Switch", which is a bit of a misnomer as its required for hot water too. The purpose of the switch is to confirm that there is adequate flow of water around the boiler and CH system. The switch is enclosed in a clear plastic cover so you can see into it. It is attached to the brass 'flow group' on the left hand side underneath the boiler.

When hot water or CH is called for, a small pin extends out from the flow group and trips the switch. If the level of flow is insufficient, then the pin does not extend out enough to trip the switch and the boiler locks out.

look carefully at the switch (probably need a small torch) when someone calls for hot water or CH. you should see the pin extend out and trip the switch.

p.s. before you look at this, first check that the boiler is registering the need for DHW by checking that the red LED lights up on other microswitch attached to the 'return group' on the right hand side

 

[Toxtoth]

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