Do I need a new printed circuit board (PCB) Baxi DuoTec 28HE

[Brokenfloat]

Can anyone help with diagnosis of an electrical problem with my 2 yr-old Combi?

I think I am looking at a new PCB at £115, but I would like to avoid paying a heating engineer's call-out of £55 if it is inevitable that he'll just confirm that yes, I DO have to spend the £115 too!

Actually if I wasn't so 'thrifty' I wouldn't be in this mess. I bought the integral electrical/mechanical timer for my Baxi DuoTec 28HE and decided to fit it myself. To be fair it was as easy as pie BUT as luck would have it the timer was faulty (wouldn't even turn manually). While I was mucking about trying to confirm to myself that it WAS faulty, I rather cleverly touched the timer's 'live' terminal against the pump casing. Oh dear.

This blew the two 'internal' 2amp fuses knocking the whole boiler out.

I replaced these, but have only got a partial fix. Essentially the boiler now fires and delivers DHW, but although the CH temperature control registers as working on the digital display, it does not fire up the boiler.

I don't have a room stat and have always previously controlled CH simply by manual use of the CGH temperature control. However, now that I have removed the timer and reinstated the connections as before, the CH temperature control no longer fires up the boiler as previously.

A second problem is that when I tried fitting a new replacement timer, the live and neutral cables don't appear to be powering it to turn. (This second timer itself does work - I took it out and ran it via a plug into the mains).

Is there any alternative 'fix' that I can consider before going for a replacement PCB?

The pump itself seems to be working OK when the DHW is running. I've checked with a screwdriver and it is free-running.

The radiators appear to remain cold even when the DHW is running (I wouldn't have expected any different but have seen this mentioned on related threads...).

As a desperate attempt I have tried replacing the NTC sensor. No joy.

I suppose there isn't another 'blown' integral fuse tucked away somewhere...?

I'd be really grateful for any suggestions - even if it just gives me some certainty that a new PCB is inevitable. Thanks in advance.

 

[Agile]

You might have damaged the PCB but it may just simply have no call for heat.

You may not like this, but your experiences indicate to me that you may be a liability to boilers and your desire to save money may be costing you more in th elong run.

It seems a very cheap engineer who diagnoses a fault and fits a new part ( maybe on a second visit ) all for just £55. We charge £84 in our local area.

Tony

 

[bengasman]

Methinks you have proven to do more harm then good when repairing boilers. Do your family a favour, and get a pro to do it.

 

[Brokenfloat]

You might have damaged the PCB but it may just simply have no call for heat.

You may not like this, but your experiences indicate to me that you may be a liability to boilers and your desire to save money may be costing you more in th elong run.

It seems a very cheap engineer who diagnoses a fault and fits a new part ( maybe on a second visit ) all for just £55. We charge £84 in our local area.

Tony

Thanks Agile

Taking your relevant comments (thanks) in reverse order:

I wish I had any reassurance that £55 would cover the full diagnosis and fitting of new parts! That is the basic fee; maybe I'll check what activities would be 'on top'.

I could have paid £55 for having a timer fitted, I guess. As it turned out, combined bad luck (the faulty part) and bad practice (fair dos) DOES look like it's been a false economy to DIY on this occasion. I still think that £55 for fitting the integral timer still looks fair game for a saving to me. In the 'long run, I'm very confident that I've saved massively through all varieties of DIY - but there are setbacks and there are limits, agreed. This isn't Money-Saving Expert forum though is it? Your point is well-made and gently-put! Thanks.

Although it might run counter to your 'caution', what I would find really helpful would be an explanation of what component or components provide the 'call for heat' - the potential simple explanation that you refer to... If not MSE, it IS a DIY forum

I should add that I already do have a heating engineer booked to come out later this week... similar threads discussed the possibility that they might recommend a new PCB unnecessarily...

What do you think? Would you possibly help again here...?

 

[Agile]

A call for heat is a voltage applied or two contacts joined together supplied from a timeclock and external components like a room stat.

The PCB then provides the heating.

Testing that aspect needs electronic test equipment and experience.

Tony

 

[Brokenfloat]

A call for heat is a voltage applied or two contacts joined together supplied from a timeclock and external components like a room stat.

The PCB then provides the heating.

Testing that aspect needs electronic test equipment and experience.

Tony

Hi Agile

Quick response really appreciated - thanks.

As I posted originally, I don't have a room stat so no problem with contacts there.

I also removed the timer reinstated the original wiring which essentially by-passes any problem with timer contacts, doesn't it? (Admittedly I appear to have disabled the current to the timer - I am assuming that this will be either the wires themselves (unlikely?) or the PCB into which they are plugged at the other end)

Am I wrong to assume therefore that the only 'call for' heating would come from the CH temperature control dial? Or are there any other 'contacts' integral to the boiler? Since this dial itself appears to be integral to the PCB itself, are there any remaining possibilities that could result in the boiler not firing for the integral CH temp control whilst it DOES fire for the integral DHW control?

As stated, both controls do register on the digital display...

btw this is my first post and I haven't yet worked out how to respond without including the previous quote.

 

[DP]

OP, I have internet issues at present, so cannot download your boiler manual. Looking at Platinum instruction which may or may not be similar to your boiler for termination of programmer or roomthermostat, I see two black wires which you could loop to see if boiler fires for central heating. Look at the boiler mainual. You will see frost thermostat does this to start the boiler running when it gets too cold. Therefore, linking these terminals would initiate a demand for central heating.

If you miswired the controls, 2a fuse would blow but cannot see anything else going up in a puff of smoke. Controls are at 240v for all the boilers of this type I have looked at so far. Do check before try anything.

There are boilers which operate at lower voltages for system controls. Applying 240 volts on these, would certainly cause damage to control boards,

 

[Agile]

You click the " reply" button lower down the page.

The time clock produces the first call for heat so some of its connections need to be present or linked out.

The call for heat is external to the PCB.

Tony

 

[Brokenfloat]

Thanks DP and Agile

DP I think I have in effect carried out your recommendation to loop the two black wires and bypass the timer.

The boiler comes like this as it is supplied without the timer (the optional extra with which I started this mess). The L and N feed wires terminate in a connecting block and the two black wires form a loop. I took out the timer and reinstated this arrangement.

Previously the CH temperature dial was (as far as I am aware) the only relevant control initiating the demand for heat (for the Central Heating). (btw I was VERY impressed with the degree of control that this simple mechanism gave over the temperature round my flat with this boiler)

Having unwittingly tried your experiment, the bad news is that the boiler does not fire up. ( See previously - it does fire for DHW)

To be fair I should make it clear that I didn't miswire the controls. They were correctly wired when I stupidly allowed the live terminal of the timer to touch against the pump casing and short the whole thing. It broke part of the terminal block housing the 2amp fuse as well as blowing the fuses.

Agile, am I right to think that reinstating the wiring meets your condition that 'The time clock... connections... need to be linked out'?

What puzzles me is if the call for heat is external to the PCB, what is there left to be calling for heat?

As far as I can tell the only demand originates with the CH temperature dial - which in this boiler appears to be integral to the PCB anyway.

ARE there any other components other than the PCB that could be responsible...?

Thanks again all - it is all helpful.