M30100 DHW fault

[beng77]

Hi,

For quite a while now my ISAR M30100 has been playing up. Everything works, but every so often the boiler briefly fires up and displays a D on the LCD as if hot water is being drawn off. This can happen every five minutes and is worse after running a bath. There are no leaks and no dripping taps. Any ideas?

I'm thinking the PCB is on it's way out but don't want to replace it if that's not the fault.

Also does anyone know if there's an alternative PCB available as the one listed in the service manual 170930 is proving hard to source. For example there are a few 172490 PCB's on ebay. Would one of these do?

Thanks,

Ben.

 

[Agile]

Could it just be correctly following its DHW preheat but that would be a "t" displayed?

If it really is giving a "d" then the implication is that there is a leak in the hot water pipework.

You can check the latter by leaving the boiler unused for a couple of hours and feeling the hot water out pipe say 600 mm away from the boiler and this should not be hot !

If it is then turn OFF the cold into the boiler and that should stop the random firing.

Tony

 

[gas4you]

If it is then turn OFF the cold into the boiler and that should stop the random firing.

Tony

I would try this first to eliminate any leaks or drips that may not be visible. It it stops it has self diagnosed the leak for you.

 

[beng77]

It does display a 't' on the display when it needs to heat the plate up, but mostly a 'D' as if water is being drawn off. I'll do the tests, but this has been going on for quite a while now and i'm pretty certain it's not the pipework. It's only a small bungalow and all the hot water pipes are in one wall in the center.

It tends to get worse after running a hot bath. Usually an hour or so after running it it starts playing up. The only cure is to switch it off for an hour, but recently this doesn't make much difference.

Thanks for the suggestions so far.

Ben.

 

[Agile]

Do the test and then we will advise you further.

My first simple test needs no tools or technical knowledge.

Dave and I would jump to the second as we have the tools and knowledge.

Tony

 

[beng77]

Here goes. Switched it on at 6pm after being off all day. After it settled down and the LCD displayed '0' I drew off a small amount of hot water to make sure I'd be checking the right pipe from the boiler. Nothing happend for three hours then finally it went through a pre-heat cycle and displayed a 't' before going back to '0'. The DHW output pipe remained cool after it had chance to discipate the heat from the initial hot water check.

All went quiet for another hour and a half. Decided to do the washing up knowing this is the sort of thing which sets it off. It's now midnight, the pipe is cold again and the boilers been silent since the washing up. I'm not reading too much into its good behaviour as it goes through phases usually spured off by running a bath or drawing off a reasonable amount of hot water.

Will watch it closely again tomorrow and report back.

Ben.

 

[beng77]

Yesterday went the same as the night before, nothing to report really. However today the boilers been on all day and tonight it's started display a 'd' and breifly fireing the burner every 20 minutes or so. The output pipe is cold and to be certain I've closed off the isolation valve to stop the cold water feed. Pretty sure it's not a leak.

Any ideas were the fault lies?

Thanks,

Ben.

 

[Agile]

Your boiler senses a DHW demand when the DHW sensor goes cold ( from incoming cold water ).

But that same sensor also is used to control the DHW preheat.

I can only guess that the PCB intreprets the actual value as determining which action is required but I would have to check that by substituting a pot for the sensor. It could also be determined from the rate of change downwards! Modern software can be quite clever.

Perhaps one of the Ideal engineers can offer further information but many of they just concentrate on what to do to fix the boiler rather than the more detailed aspects of their operation.

To try to fix yours you could start by checking the connector on the DHW sensor in case thats making poor contact.

Substituting a fixed resistor of say 3 k to simulate a hot plate HE would bypass the DHW sensor. That would then enable the PCB to be checked as the PCB may be wrongly interpreting the sensor. Most faults like this are the sensors though.

All this may be beyond your capabilities but thats what I would be doing! Some of the Ideal engeneers on here may have other suggestions too. Ideal probably have a fixed price repair service.

Tony

 

[beng77]

Hi Tony,

I've previously checked the connection to the DHW thermister and even had a mutimeter on it to check if the resistance matches up to the figures in the manual for a given temp. All looks ok. You have confirmed my suspicion that there are only two parts to the problem, the sensor and the PCB. The sensor tests ok which only leaves one part.

I have noticed there is a mains power supply filter. If this was failing would it cause any strange behaviour?

Thanks again,

Ben.

 

[Agile]

Sometimes the sensors have faulty connection welds inside and give intermittent and eratic results usually as temperature changes.

Since the sensor is so cheap and easy to simulate by a fixed resistor as I suggested before, that is what you should concentrate on first before you contemplate a new PCB at about £160 !!!

Tony

 

[beng77]

Just to close this thread off, in the end I went out and bought a 172490 PCB set the jumpers to match my existing one and installed it last weekend. Been switched on and working perfectly ever since.

Ben.