Bad kettling

[tabbypurr]

An old boiler (30 years or so) has been kettling increasingly over time, an d is now doing so badly. It now kettles strongly while the flame is on, rat her than when the pump stops. Previously it has been addressed by turning d own the primary stat and fitting a pump overrun. Primary stat is at minimum . The boiler weeps a bit at times, and is kept sealed up with sodium silica te in the primary, that's been in there for at least a decade. It still pas ses its tests, and replacement is planned for next year. But the level of k ettling is now unacceptable.

I can only presume the cause of the problem is reduced flow. The question i s why. Sludge? An ever growing lump of waterglass inside the boiler heat ex changer tubing? Gradual pump impellor disintegration? Something else? How c an I find out, short of major dismantling?

All but one rads have a TRV. It's an S plan system.

NT

[polygonum]

Some months ago, our very, very old Kingfisher boiler had been making quite a lot of kettling noise. I separately replaced both the three-way valve and the pump. Shocking how bad both were inside - amazing they were working at all! Kettling reduced dramatically. I think the biggest effect was the pump - I used an Alpha 2.

Thankfully, that system is no longer our responsibility.

[harry]

and is now doing so badly. It now kettles strongly while the flame is on, r ather than when the pump stops. Previously it has been addressed by turning down the primary stat and fitting a pump overrun. Primary stat is at minim um. The boiler weeps a bit at times, and is kept sealed up with sodium sili cate in the primary, that's been in there for at least a decade. It still p asses its tests, and replacement is planned for next year. But the level of kettling is now unacceptable.

is why. Sludge? An ever growing lump of waterglass inside the boiler heat exchanger tubing? Gradual pump impellor disintegration? Something else? How can I find out, short of major dismantling?

Kettling can be caused by several things. One is local hot spots on the heat exchanger. Caused by silt, corrosion and scale on the wet side. (Prevents heat from transfering). A chemical cleaning might fix it. Might also start a leak or two!

[harry]

, and is now doing so badly. It now kettles strongly while the flame is on, rather than when the pump stops. Previously it has been addressed by turni ng down the primary stat and fitting a pump overrun. Primary stat is at min imum. The boiler weeps a bit at times, and is kept sealed up with sodium si licate in the primary, that's been in there for at least a decade. It still passes its tests, and replacement is planned for next year. But the level of kettling is now unacceptable.

on is why. Sludge? An ever growing lump of waterglass inside the boiler hea t exchanger tubing? Gradual pump impellor disintegration? Something else? H ow can I find out, short of major dismantling?

Additionally, you need to add chemicals to the water in the system system w hich reduces corrosion and also reduces kettling in some cases by increasin g the boiling point of the water, (read instructions).

[John Rumm]

Lob a can of sentinel boiler noise reducer in there... probably about the only amount of effort worth wasting on it.

[tabbypurr]

That won't stop it deteriorating. I suppose the only way to really find out the cause is to dismantle each item to see what's in good shape & what isn't. I hate plumbing.

NT

[Davey]

When our system started to make the dreaded noise, we got a local plumber with a good reputation to clean the system with a pumped chemical cleaner. It's now wonderfully silent, and has inhibitor in it.

Money well spent, in our opinion.

[charles]

we had our system professionally cleaned a few years ago. It all went silent. Despite using inhibitor and noise reducer , kettling is now back.

[tabbypurr]

I'm told it's been quiet today. So I'll get a magnaclean type filter on it, and empty it when I'm up there.

NT

[John Rumm]

If its being replaced anyway, how much do you care?

The causes are typically heavy scaling or other contamination of the HE inner surfaces, or something that is producing inadequate flow (obstruction or failing pump). You could replace the pump, check the valves, and then flush the system, and finally give it a full de-scale. Although I suspect that if I were going to that much trouble I would replace the boiler and any knackered looking rads at the same time.

[tabbypurr]

Replacement is due in a year. I really don't want to do it now if it's avoi dable, so much else to do. New pump & magnaclean are due for when the new b oiler goes in anyway, so I can try and fit those in as soon as poss. Maybe if I don't post here for a month I'll have saved the time to do it! Did I m ention I hate plumbing?

Would cleaning chemicals dissolve the waterglass? If so, it's gonna leak ba dly. If not, it might stay part blocked.

NT

[charles]

I've been usinga Screwfix product. Is that a mistake?

[polygonum]

I too used a Screwfix product and it worked fine. When I had to partially drain the system to replace pump, then the three-way valve some months later, the fluid was almost water-clear. A huge contrast to when I first cleaned the system out and put inhibitor into the system - many years ago.

[Martin Brown]

Me too. At least electricity stays in wires but water has a very bad habit of going all over the place especially where you don't want it.

Particularly the gungy stuff running around inside a CH system on its last legs is a pretty horrible black sedimented gunge. Is there any trapped air somewhere near the boiler encouraging it to kettle?

I was amazed at the state of a boiler in a hard water area after it had failed spectacularly. I have a picture somewhere but it had massive encrustations of limescale and thicker slabs on the bottoms of every heat exchanger tube. It was a really weird design not like UK ones.