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).

So far I've checked the following:

- Water pressure looks good at around 1.5 bar
- Gas pressure looked good at 11mbar from recent service
- 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!

Richard

 

[Agile]

Just as the diagnostic code indicates the primary flow switch is not being activated on hot water!

Quite a common problem on this model as they are getting older and not having the system kept in good condition.

Tony

 

[joe-90]

I had a similar fault once. It turned out to be the flow/pressure switch in the DHW supply. It's there to stop the boiler firing up in the absence of water and to fire the boiler independent of the heating. Being as your boiler works for hot water when the heating is working I'd check that if I were you. The part cost about £15.

 

[Agile]

Joe is a decorator and has no knowledge of boilers!

Your boiler does not even have the switch he is trying to suggest as the fault!

He has a hatred of boiler engineers and tries to disrupt this part of the forum. I dont know if he made that posting to try and be helpful or just to cause confusion. Usually its the latter.

Tony

 

[joe-90]

Similar problem - flow switch. Call it what you like. Something to look for isn't it? Only giving the OP something to consider. I'm not a decorator any more than Tony is VAT registered.

 

[Ray84]

Richard as tony says its a faulty flow switch. I think on the mini when the hot water taps opened a small red led inside the boiler should light then the flow switch is operating properly
no right led - faulty flow switch (maybe choked or has a small hole developed on the diaphgram

Ray

 

[Agile]

Whilst Joe has no knowledge of boilers Ray is trying to be helpful but is also confusing the issue by wrongly describing the problem.

The problem is NOT the DHW flow switch as you already know and stated in your first post.

The problem is with the boiler primary flow switch!

Tony

 

[Ray84]

yeah sorry jumped in and decribed what you already know.

primary flow switch/pump proving switch.
Cheap enough repair if you get the right person the diaphragm is about £5 and likely to be that or choked up
(99% doubt its the pump but is related to it)

Ray

 

[Agile]

The problem is unlikely to be fixed by just changing the diaphragm!

I dont think I have ever encountered a failed diaphragm although I have damaged some checking/removing them.

Tony

 

[Toxtoth]

Thanks guys!

I assume the main switch itself is fine because the CH demand trips it properly.

So that leaves one of two things I reckon:
1. block heat exchanger not allowing enough flow through
2. broken/clogged diaphram not pushing out enough

do you think am i on the right lines? i will visually inspect the main switch tonight

its just weird that the DHW works fine if CH is already being called for (i.e. the flow rate is enough once the pump is already circulating??). would this make sense?

 

[Agile]

As I said its almost certain to NOT be the diaphragm.

A blockage in the plate HE is a possibility but other blockages are quite likely including the pump performance.

Once the switch is activated ( as in CH ) the hysteresis will often allow it to stay made for DHW whereas DHW on its own would not be sufficient. It may sound weird to you but its just a logical situation when you know whats happening.

Tony

 

[mburton2]

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).

So far I've checked the following:

- Water pressure looks good at around 1.5 bar
- Gas pressure looked good at 11mbar from recent service
- 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!

Richard

Did you manage to resolve this?...I have a C24 doing exactly the same.
The Change-over solenoid (Three-way valve motor) has been replaced, and the Diverter-valve has had all moving pars replaced (service kit).
I have just bought a diaphram/switch membrane which is being fitted tonight....am I hoping too much that this will fix the problem?

 

[Agile]

I do try very hard to describe what the problem is likely to be. Unfortunately people are either very selective with what they read or totally unable to understand simple aspects of boiler operation.

Merely replacing parts as you are doing is unlikely to solve the problem in most cases.

Tony

 

[mburton2]

Ok...diaphragm replaced..made an improvement, but still temperamental. ..
The old diaphragm was fairly hard/brittle, BUT, I would of thought it would have been functional.

Having seen the comments above about the pin not quite activating the micro-switch, I put a little kink in the flat-metal part of the switch-assy..so the pin didnt have to move quite so much to activate the microswitch.
Nearly all seems to be ok now....when hot water is demanded, the boiler fires up as expected..The tenant no longer needs the heating to be active, to get hot water. <result>

The only thing now is, the hot-water isnt coming out as hot as it used to...its hot enough...but not as hot as it was/should be?

 

[Tibbot]

The only thing now is, the hot-water isnt coming out as hot as it used to...its hot enough...but not as hot as it was/should be?

That's because the bodge you've passed off as a repair cannot cure the underlying problem. But still, as long as your tenant's happy.