Will chemical cleaner get into the gravity DHW flow/return?

[chrisw99]

I have a traditional old-fashioned set up, boiler with two sets of flow/returns. One goes to the CH pump/radiators. The other by gravity up to the coil in the hot water cylinder.

If I was to add any kind of chemical - cleaner, inhibitor, etc, the CH pump would pump this all around the CH circuit, but would it also get up the DHW pipes as these aren't pumped?

I'm assuming (remembering my basic O levels seeing colour liquids rise in a beaker) that it would get up there via natural convection, but would there be enough of a flow to be effective?

 

[JohnD]

Whatever additives you put in the water will get mixed and circulated through the entire system. The CH and the HW circuits mix together in the boiler.

I did that using X400, and got a lot of old sediment out. A few months later I converted it to fully pumped, and a lot more black sludge came out for a short time. It would have been loosened by the chemical, but the flow in the HW circuit was too slow to wash it away.

I had already fitted a system filter so I could easily see how much it trapped.

 

[Diy-mañana]

Hope its not a primatic cylinder,pop up the loft and make sure there are 2 water tanks,one big,one small both should have water in them.

 

[chrisw99]

Whatever additives you put in the water will get mixed and circulated through the entire system. The CH and the HW circuits mix together in the boiler.

I did that using X400, and got a lot of old sediment out. A few months later I converted it to fully pumped, and a lot more black sludge came out for a short time. It would have been loosened by the chemical, but the flow in the HW circuit was too slow to wash it away.

I had already fitted a system filter so I could easily see how much it trapped.

Interesting, thanks. X400 is what I intend to use, as I suspect my HW circuit is similarly full of sludge. The time taken to heat the cylinder is taking much longer than it did 15 years ago, always meant to investigate but things have come to a head now, it's taking so long to get the heat away from the boiler that it cuts out and starts short cycling.

A bit worried you needed a pump to get the sludge out once loosened, I won't have that luxury. Got a few ideas though... after the X400 has had 4-6 weeks will drain the system out but leave the feed filling for a bit to give a bit of flow. A bit of extra pressure from a mains hose down the expansion whilst doing so may help. And a few convenient taps of the pipes with a rubber mallet may shift.

Also another idea, I notice when the HW only is on and both pipes are red hot (which does happen, eventually, just takes a long time) and I then put the CH on, both pipes immediately go cold, the pump must have created a bit of suction to pull it into the CH circuit... this may be enough to pull the sludge after a few weeks with X400?

If no joy after that, may try the more aggressive X800 for a day and repeat the above.

Unless anyone has any better ideas... and yes, replacing with a Combi is one option

 

[JohnD]

converting to fully pumped is an option.

gravity hw is very slow to heat the cylinder, especially if the pipe run is long or has horizontal sections.

 

[chrisw99]

converting to fully pumped is an option.

gravity hw is very slow to heat the cylinder, especially if the pipe run is long or has horizontal sections.

I have a plan to replace the boiler in a couple of years with a combi as I'll be rebuilding the garage wall where the boiler is currently located, so don't really want to go down converting to fully pumped, or paying £££s for a powerflush, if I can get a quick fix that will last a couple of years. Also the blockage could be something else that a pump wouldn't sort I guess.

Yes it's always been slow, but now it's excruciatingly so. Once the boiler cuts out after 2-3 mins from cold, the first 3-4 inches of the pipe near the boiler are too hot to touch. 3 feet away it's still cold for another minute. Definitely used to be faster than that! Probably 5-6 mins before the heat actually gets up to the cylinder.

And probably about 2 hrs before the return pipe gets hot.

Another option I missed is back filling from the drain cock with a mains hose?

 

[JohnD]

How much suffering are you willing to endure, to avoid converting it to fully pumped?

 

[chrisw99]

How much suffering are you willing to endure, to avoid converting it to fully pumped?

I was told it would be expensive to do so. Maybe I should look into it. Got to be worth a try with the X400 first though, it could shift it at the first attempt.

 

[JohnD]

post some photos of the pipe layout round the boiler and the cylinder.

 

[chrisw99]

 

[chrisw99]

Looking at the photo of the cylinder, I guess another easy option once the X400 has had some time will be to drain the system and disconnect the top connection into the cylinder, and then just stick a hose into both sides of the connection in turn. At the very least it would identify if there was a proper blockage if it doesn't drain out the drain cock.

 

[Echo the husky]

Is it me or has that upper nut been soldered?

 

[Steelmasons]

Is it me or has that upper nut been soldered?

Looks like silicone to me.
The coil will be blocked @ the top around the union , undo the union nut and clear the blockage.
Gravity hot water cylinders used an annulus as opposed to a coil.

 

[ianmcd]

Looks like LSX leak sealer that lazy incompetent barstewards use.

 

[John D v2.0]

If the pump is causing suction in the hw circuit, one way to dislodge things would be to close any isolator between the boiler and where it tees off between dhw and ch,turn off the boiler heat/electric, then run the pump on max (without the boiler) to circulate round the hw circuit. Then do your hammer tapping and cleaning out the filter etc.
Does it have a combined or separate feed/expansion pint on the hw pipework? If separate, The thing you have to watch is pulling in air through the expansion pipe or pumping over, you could always cap it *temporarily* while you're doing that pumping process.
However your cold water probably has more pressure and flow then your pump, so may be more effective if you can cobble that up.
Good luck!