Ball park repair estimate for blocked heat exchanger on a combi?

ChasingtheWelshdream

We have an independent engineer coming out in a few days but in the meantime I just wondered if anyone would have an idea of expected repair costs for a 9 year old boiler?

Baxi duotec combi, appears to have blocked/dirty heat exchangers which is giving error code E125. We have done some troubleshooting and everything points to sludge getting in. Meh. 

I'm bracing myself for a large bill, but is this something that anyone has experience of being fixed, and a very rough cost? Or is it something that could end up uneconomic to repair?

Edit: I’ve found that heat exchange replacement can be around £500 (ouch!) but what I am less sure of is whether any sludge/blockage can usually be cleared. 

ThisIsWeird

Are we talking mainX or P2P?
For main, unless you have a service contract or can get a fixed price repair, it usually means it's not worth fixing. :-(

ChasingtheWelshdream

ThisIsWeird said:

Are we talking mainX or P2P?
For main, unless you have a service contract or can get a fixed price repair, it usually means it's not worth fixing. :-(

Not a clue, the error code is a circulation problem, which could be caused by a blocked exchanger. That’s as far as we know until it is looked at.

We suspect sludge as we drained the system to move a radiator and the water was not great, even though we topped up inhibitor last year.   For the first time the magna filter had metal deposits on it, when it is usually pretty clean. It looks like some sludge/rust has got into the exchanger when draining/filling the system as everything was fine beforehand. We’ve done this several times over the years and have never had an issue before.

No service contract, but we’ve had it serviced every year by independent engineers. 

Sad times 😕 

GDB2222

Some Baxi boilers have a 10 year warranty, but otherwise budget £300+. Baxi do a fixed price repair for £417. Ouch!

ChasingtheWelshdream

Big ouch!

However......(and this is being said rather tentatively as I am only a DIY mum. I make no claims that this is the correct way to do anything).

Everything is working again! Whilst crying into my cup of tea and imagining my meagre DIY savings dropping to zero, I watched a few more Youtube videos, read a couple more articles and decided I may as well give it one more go. One of the circulation issues  hat gives that error could be an air lock, which I had been convinced there wasn't. But I thought, go back to the beginning, think what I have 'done' over the last week, then 'undo' it and try going through the troubleshooting again.

Re-checked all radiators. Re-checked the filter. Turned on some rads that I had left turned off (which are due to be taken out soon, so I had decided to leave the valves closed, not thinking it would cause a problem).  Re-bled everything.  Tentatively tried the heating. Nope, no joy.....but...but.... it wasn't giving the error code. Or making the horrid noises.... Which was a slight improvement surely?

With the water set to 60 degrees, it would call for heat but rapidly climb above 60 and cut out when it hit 70. Overheating. The flow would get hot, but the return would stay stubbornly cold and then the flow would cool down shortly after the boiler cut out. So still a circulation issue, still a blockage. Dammit.

But hang on, at least with slightly happier sounding boiler. As a last ditch attempt, I wondered that if it were cutting out when it was set to 60, logically, what about setting the temperature to max, and see if it would stay ignited. If it did, could it push a blockage along? With the hope that it would shut down if everything went Pete Tong, I upped the temperature. 

....

10 seconds..... 20..... 30.... a couple of small knocking sounds and I was braced for the cut out. Nope, still igniting. The flow still hot. No more knocking noises. Could this actually be working?!

My son calls out his radiator is making a funny noise (his is first on the radiator run). Dammit. Runs to his bedroom. Hang on, that noise is just water circulating. The radiator is getting hot. His RETURN pipe is getting hot! Water is circulating!

Cue me manically running around every radiator and yes, disbelievingly, they are warming up!

Runs back to the boiler and.......the return is finally hot! The circuit has been completed!  Run round again and find one rad needed bleeding, so against all odds that was (I assume) an air lock being disgorged. The airlock I assumed wasn't there. 

So I turn down the water temp back to sixty and spend 10 minutes staring at the dials, bracing for it to conk out. Temperature stable. Pressure fine. Noise fine. Pump fine!

Tentatively turn on the hot tap, waiting for it to decide to die again.

Well blow me down, not a peep. Just a lovely, steady, STABLE flow of hot water. 

Just had a celebratory shower. 

I am not cancelling the engineer as it all needs looking at and is due a service, but I am now far more hopeful that I may have some pennies left to finally buy the last radiators needed to finish the great radiator shuffle project, that has lasted for at least 2 years too long. 

GDB2222

That is really good news. 

Do you have a magnetic filter on the system? 

ChasingtheWelshdream

GDB2222 said:

That is really good news. 

Do you have a magnetic filter on the system? 

We do indeed, a magnaclean. That was the reason we assumed the exchanger was blocked with sludge. The filter is usually rather good - I check it every 6 months. Before and after the heating season. 

After draining down last week it had a bunch of metal particles on it, more than I had ever seen. Proper flakes, not just ‘sludge’. This coincided with the dirty water on the system drain down, so we assumed that something bad had got into the exchangers. Before it went kaput I dosed with X400 to help give the pipes a clean with the intension of flushing through in a couple of weeks. Hopefully that can now start circulating. 

I know blocked exchangers can also cause other issues and internal leaks so the engineer can take a good old look at the innards.

ThisIsWeird

Phew!

Looking up E125, it does indeed suggest a circulation problem, but the most common cause is low system pressure - but undoubtedly you'll have checked this first?

Other potential causes Baxi mentions include air locks, as you suspected, and a failing pump. It's hard to figure out where an air lock could exist that causes this - a sealed system like this with a pretty powerful pump would usually shift anything like that along, until it ends up inside a rad - have you tried bleeding them all?

In a combi, it can also be caused by a sticking divertor valve, which doesn't shift fully into the CH mode, so the flow is partially blocked. This can be more obvious when you are drawing DHW, and you find the CH flow pipe becoming unusually hot too, which it shouldn't be.

Tbh, for this to be caused by the MainX would be unusual, certainly due to sediment, as that would involve a shed-load of material inside it, whereas your Mag Filter has been catching only smallish amounts up until now. And such sludge would normally block the P2P exchanger first, which has tiny waterways inside it, and the symptom here would be the DHW fluctuating hot and cold during, say, showers - that hasn't happened?

Whilst it's possible that the MainX is the culprit, I'd suggest it's unlikely, and there are far more obvious suspects such as the pump and diverter valve - both should be cheaper to fix, if so. Or, even an unusual airlock.

Pressure ok? What's it set at? All rads bled ok? Any air?

ChasingtheWelshdream

All pressure etc is good, and as I discovered above, there was an air lock pushed out once the boiler could stay firing rather than cutting out instantly.

And such sludge would normally block the P2P exchanger first, which has tiny waterways inside it, and the symptom here would be the DHW fluctuating hot and cold during, say, showers - that hasn't happened?

That is why we called the engineer in the first place and why I want him to check everything inside. The hot water is back to being unstable this morning, but at least doesn't cut out. There is still an issue but hopefully not as expensive as previously thought.

ChasingtheWelshdream

Just an update if any interest. It was a stuck air admittance valve (I forget the name) - total cost for a replacement part including call out - £85. Happy times. 

ThisIsWeird

That's a result.

I was about to mention that as a possibility...

Not.