Ideal mini c28 - Intermittent fault, now noisy also.

[Farfromideal]

Hi everyone.

We have an Ideal C28 mini combi in our house, but it's not been right since we moved in.

Using DHW alone, it has been tripping/locking itself out, and the tap water was never really hot. During winter though, we've got by quite well as we found if the heating was on high, the water from the taps was much hotter and cut out much less frequently.

The CH also occasionally trips when there isn't DHW demand (nights).

When these faults were happening, the boiler still sounded normal, it just needed the demand cut to reset the flashing green light, after which it would work again. More recently though, there has been a buzzing sound from the boiler and it is having trouble igniting. To me it sounds similar to a PC fan hitting its case.

Unfortunately cutting demand does not reset this new problem.

When it does ignite, it can go for a few seconds or a few hrs at a time.

I have uploaded a video of it in action (CH was on demand only) here: youtu.be/7eehFjQYL0w

We had a guy over before winter to look at it, and he suggested it was a blocked secondary heat exchanger, so we agreed to have it replaced, but for some reason he went silent and didn't get back to us, so it never was changed. I didn't have much faith in his 2 minute hands-off diagnostic anyway.

If the secondary heat exchanger is blocked, I'm thinking there must be other faults also.

Can anyone here advise what is likely to need fixing with this boiler, and whether it's actually worth tackling, or better to just get a new one as it's 13yrs old now.

The serial no. is N023270304.

Thank you!

 

[Farfromideal]

Sorry, I forgot to say that the noise in the video is coming from the area housing the "3 way divertor valve", "gas valve" and "DHW flow switch". It is difficult to tell which it is, as I do not wish to stick my head much closer when its running, but if I had to guess, I'd say it seems to be from the bottom of the gas valve.

 

[Agile]

It sounds as if you have multiple faults although none very serious.

I fix a lot of that model myself, but generally they are not that well liked by many engineers.

My advice is that they are totally fixable if only you can find someone who specializes in repairing rather than installations.

Tony

 

[Farfromideal]

Hi Tony,

Thanks for the reply.

I had another listen today, and it actually seemed like the noise was coming from below the plastic guard that houses the PCB......but is there anything on the pcb, or anything else in that boxed-in area, that could even make such noise?! If I touch the plastic when the boiler grinds/buzzes, it feels like something is hitting the plastic from below.

Does the PCB have a fan, perhaps?

Is it worth me trying to remove the plastic cover to have a look, or should I leave it well alone?

Thanks.

 

[Agile]

There are three relays on the PCB and although very rare I suppose one of them could be buzzing at 100 Hz.

I would be using an oscilloscope to check the smoothing of the 24 v bus supply.

Tony

 

[DP]

There are three relays on the PCB and although very rare I suppose one of them could be buzzing at 100 Hz.

I would be using an oscilloscope to check the smoothing of the 24 v bus supply.

Tony

Tony, why not the ESR meter?

 

[Agile]

I don't see any application for the ESR when I want to know how well smoothed the DC is.

If I was then going to repair the PCB then I could use the ESR meter to check the smoothing capacitor.

But generally I like to replace faulty PCBs with new ones.

 

[DP]

So why bother using the 'scope?
An apparatus I do have but in 23 years repairing boilers have never had the urge or need to use in the field.

 

[Farfromideal]

I think it is the PCB buzzing.

I took off the 2 front screws that hold the plastic cover down to take a peek inside, and just before the boiler gave up trying to ignite, there was a small blue electric spark from the same area the buzzing seems to be coming from (somewhere behind the nearest relay).

With it quite likely there are multiple faults with this boiler, am I best just signing up for annual boiler cover from the likes of BG or SSE, or just getting a new boiler?

Cover seems to wok out at around £200 for the year, which isn't so bad as the PCB replacement would prob come to that alone, looking at the part prices.

 

[Agile]

So why bother using the 'scope?

So how would you check for ripple on the supply line ?

 

[Agile]

Cover seems to wok out at around £200 for the year, which isn't so bad as the PCB replacement would prob come to that alone, looking at the part prices.

That would be one solution.

But I would still favour an independent engineer. But it would have to be one of the few who really understand boilers and who have reasonable charges.

Whilst I don't know what all your boiler problems are, if I was repairing it then I would not expect the total cost to be much more than £200, perhaps even less depending on how I dealt with the PCB.

Tony

 

[DP]

So how would you check for ripple on the supply line ?

After reading your post, dug out a duff pcb for that boiler to look at the connections
If the supply was faulty, every relay would buzz. If contacts were worn, then single relay would buzz. Come across this often and have carried out temperory repairs to keep the boiler running until can return with replacement
A full wave rectification, half wave even may I add, will operate the relay without causing it to buzz. But what will not work is the circuitry employing transistors
If rectification is suspect, I would check the diodes and meter the capacitor value matches (given tolerances) to measured value

How would you deal with the pcb Tony?

 

[Agile]

With buzzing on a relay or the mod coil I would normally just know that it is likely to be a failure of the smoothing cap. The amount of buzz will vary according to the load on the supply.

But if I was feeling keen then I could view the DC bus supply on an oscilloscope.

Or even try the bodge of measuring AC voltage on it through a cap.

A 100 Hz buzz can only be derived from an AC supply.

On the Biasi 24S, where smoothing deficiencies are getting rather common due to the age of the boiler, the mod coil will buzz quite loudly well before any circuit malfunctions become apparent. I have heard of RGIs changing the gas valve for that fault!

In the case of a failing smoothing cap they will either feel warm ( due to high ESR ) or show physical damage like a bulging case.

 

[DP]

Tony you need to sit down and read what you have written
Clearly there are big omissions in your post and big assumptions too

"AC voltage through it on a capacitor"?
What are you on about?
How can you pass AC voltage through an electrolytic capacitor.

 

[Agile]

You need to think a little when I make comments on electronics.