Descaling unvented cylinder

[clemda1]

Hia guys I have a 300l unvented hot water cylinder not getting up to temperature.
Primary Flow into the coilis coming in at approx 70deg but water temperature is not getting above 40deg. Cylinder is over 10years no scale reduction so Im guessing the coil is scaled or sediment build up is preventing heat exchange working efficiently.

Customer is not in a position financially to replace the unit so I suggested a descaling using fernox ds3 (recommended by plumbing merchant)

I haven’t done this before. My intention is to first drain the cylinder and wet vac out as much scale as I can manually. While isolating the cylinder from the rest of the house use the back up immersion to get the cylinder up to temperature for a few hours. Then thoroughly cleaning by filling and draining 4-5times then running the hot water out of all outlts for good 10mins to ensure all the acid is removed.

Just wondering if this sounds like a viable plan and if anyone has experience with it.

 

[oz-plumber]

What will be your costs of doing all the works versus replacing the cylinder coil.
Drain the cylinder at the time of coil replacement and clean the cylinder that way - then no chemicals

 

[Gasmk1]

that is probably a days to 2 days labour and mats. i would say not cost effective myself. and go for a new cylinder.

 

[ShaunCorbs]

New cylinder for me aswell

But to descale it fill it full with ds3 bad stuff be careful if it’s limesca

Or x800 if it’s a layer of sludge

Also the outside of the coil could be insulated with limescale if your in a hard water area

 

[Scott_D]

Can you test the water to ensure chemicals are removed?
What if you do all the and it doesn’t fix the issue?

 

[Chuck]

Make sure you've confirmed it really is scaling rather than some heating circuit issue, for example a faulty zone valve, before doing anything too radical. Nothing beats direct visual confirmation in these circs.

 

[clemda1]

What will be your costs of doing all the works versus replacing the cylinder coil.
Drain the cylinder at the time of coil replacement and clean the cylinder that way - then no chemicals

Are you saying it’s possible to replace the internal coil on

Can you test the water to ensure chemicals are removed?
What if you do all the and it doesn’t fix the issue?

Was planning on testing ph before and after for confirmation all the acid was removed also can use a neutraliser if required.

New cylinder for me aswell

But to descale it fill it full with ds3 bad stuff be careful if it’s limesca

Or x800 if it’s a layer of sludge

Also the outside of the coil could be insulated with limescale if your in a hard water area

When you say sludge inside a hot water cylinder and you elaborate please. I was planning on wet vacuuming out most what I could prior to introducing the acid.

 

[chris watkins]

From my experience an indirect unvented cylinder will not be suffering from scale unless the domestic side has been run at higher temperatures >65 degC but if you wanted to check why not drain it & remove the immersion to inspect the inside.
It is more likely that the problem is with the water flow through the coil. You say the flow was 70C but what was the return ? and much more importantly did you feel the temperature of the hot water outlet directly off the cylinder ??
At 40 degC at the taps this if much more likely to be cross flow from a mixer, I have even had them pushing cold water back down the hot close to the cylinder.

 

[Timmy D]

With the symptoms you’ve described, I wouldn’t be looking at the cylinder. Possible but unlikely.

Ideally you need 1 or 2 pipe thermometers, confirm boiler/cylinder flow/return.

Confirm cylinder outlet temp. Confirm temps at outlets while in use.

I’d be looking for a cross over. Cold getting into the hot. Usually I find them at thermostatic showers but anything thermostatic could cause it. New cartridge solves the issue.

 

[Will]

Id check to see if it has a sacrificial anode on the cylinder to see if the flush is ok for that or maybe it need replacing to prevent further build up.