Scaled Heat Exchanger? Bad enough to cause problem?

MAXEON · Jun 25, 2019

I was recently advised "heat exchanger scaled" on a Worcester Bosch SiII combi boiler. There was a DW intermitent problem - sometimes DHW ran cold after a short while - other times worked okay. Gas installer diagnosed scaled hex. Options were to have new hex (mega cost) or replace boiler. As boiler was get ting on a bit, opted for new boiler. I retained old boiler and for curiosity, extracted the hex and cut open to see what a scaled hex looks like. See pics attached. One of the pics is of the DHW f & r pipes. I could see straight through all the pathways of the main part - including the pipes within outer pipes although difficult to show this in a photo.
Does this look like it should have caused the problem . Comments please.

Aire · Jun 26, 2019

I would say that a scaled heat ex would be faulty all the time, not intermittently. Did the engineer not offer to descale it? How much did he quote to change heat ex and how much was you charged for a new boiler?

Sharp Point · Jun 26, 2019

Yep, that hex is in a bad state. To be fair, it was on a very old boiler that could’ve been riddled with lots of other intermittent failing components. I would’ve classed that appliance as ‘beyond economical repair’
He did completely the right thing by replacing it.

Brambles · Jun 26, 2019

Craig’s comments are spot on.

That does not look like a set of tubes that have been used in a hard water area - do you know the hardness of the water feeding your boiler?

Having said that structurally the exchanger looks in poor condition

Ben-gee · Jun 26, 2019

Brambles said:
....

Having said that structurally the exchanger looks in poor condition

It is now he’s sawn it to bits!

Brambles · Jun 26, 2019

True!!!

chris watkins · Jun 26, 2019

Doesn't look scaled to me. Much more likely to have been controls side.

MAXEON · Jun 27, 2019

bogrodder said:
Yep, that hex is in a bad state. To be fair, it was on a very old boiler that could’ve been riddled with lots of other intermittent failing components. I would’ve classed that appliance as ‘beyond economical repair’

He did completely the right thing by replacing it.

MAXEON · Jun 27, 2019

The boiler was 13 years old (not what I would consider to be very old) in 2 bed flat in appartment block with reasonably good insulation mostly occupied by 1 person so not had a 'heavy duty' hard life. Water is classed as "slightly hard" by Severn Trent Water - no limescale accumalates on taps/shower head. Obviously, there is some limescale, but the layer that can be seen on the hex is about (I estimate) 0.05mm (1/20th) so I wouldn't have thought enough to affect the performance of the hex to any significant degree and certainly none of the pathways were blocked so flow rate would not be affected to cause over heating hence my suprise. I was quite expecting to find a blocked or virtually blocked hex and was somewhat suprised at what I saw hence my post to this form for views from you people in the industry.

MAXEON · Jun 27, 2019

Craig Watson said:
I would say that a scaled heat ex would be faulty all the time, not intermittently. Did the engineer not offer to descale it? How much did he quote to change heat ex and how much was you charged for a new boiler?

No offer to descale. The boiler was covered by maintenance contract (no company name to mention at present as I am having a 'dialogue' with them) but of course the hex not covered! I was just given the option of new hex or new boiler. As the boiler was 13 years old and the cost to replace the hex was around £500 inc fitting, I considered more sensible to replace boiler. I have a bit of a techy background so for interest I extracted the hex from the old boiler to see what it "scaled heat exchanger" looked like in real life!

MAXEON · Jun 27, 2019

chris watkins said:
Doesn't look scaled to me. Much more likely to have been controls side.

Having looked at the MIs for the old boiler and the flowchart for the symptoms (intermittent DHW fault) and being suprised at how unblocked the HEX looked to me, I suspect the real fault may have been a faulty thermistor or temp sensor or flow sensor?

MAXEON · Jun 27, 2019

chris watkins said:
Doesn't look scaled to me. Much more likely to have been controls side.

That is my feeling too - my eyes are telling me it was not the hex.

MAXEON · Jun 27, 2019

Brambles said:
Craig’s comments are spot on.

That does not look like a set of tubes that have been used in a hard water area - do you know the hardness of the water feeding your boiler?

Slightly hard according to Severn Trent Water and no lime on taps/showerhead.

Harvest Fields · Jun 27, 2019

Not read all posts but. You can always get a second opinion.

chris watkins · Jun 27, 2019

MAXEON said:
Having looked at the MIs for the old boiler and the flowchart for the symptoms (intermittent DHW fault) and being suprised at how unblocked the HEX looked to me, I suspect the real fault may have been a faulty thermistor or temp sensor or flow sensor?

Your problems was relying on a large company - have a read of my post in "Long boiler warranties? Worth it? "

(Shamelessly plugging his own posting

)

Scaled Heat Exchanger? Bad enough to cause problem?

MAXEON

Aire

Sharp Point

Brambles

Ben-gee

Brambles

chris watkins

MAXEON

MAXEON

MAXEON

MAXEON

MAXEON

MAXEON

Harvest Fields

chris watkins

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