Heating has me stumped

[jingizu99]

I've lurked about the forum looking for an answer to this but anything I've tried doesn't seemed to have helped, so I thought I'd register and ask.

I few weeks ago I got a dscaler and added it to my central heating system. The system is vented and has a pump. I drained enough water to get the dcsaler in, refilled the system, bled the radiators and turned it all on. the boiler fired correctly, worked for a number of minutes, then shut itself off. Water came out of the overflow before the boiler went off, suggesting the water woesn't circulating. I left the pump going in any case to try to get the solution moving. It wasn't cold so I left the solution in for a few days and drained the system. Water came out (nice and black) and I drained the entire lot, refilled, bled and switched on.

Again the boiler fired and ran for a few minutes before the overflow started pumping and the boiler went off. The only thing I could think of was a blockage somewhere or a malfunctioning pump. So I closed the valves on all the radiators bar one. Same problem. I drained the system and checked the return was empty (the pump is on the return by the way at least as far as I can make out). It was. I removed the pump and forced water through it at high pressure to clean it out. Reconnected, refilled, rebled, restarted... exactly the same thing. The pump is definitely working and switching the speed on it makes a noticeable noise difference. So now I am stumped.

The only other thing I will say is that the downstairs radiators were not heating correctly before I introduced the descaler (hence the reason). When I bleed the system dry those same three radiatiors refuse to empty even a little. I presume they are sludged up and I'll have to empty them manually - however I also presume that cannot be the cause of my trouble or the system would not actually have emptied.

Should I leave the system running for a few hours? Once the boiler cools a little it'll refire and I'll get the knocking again. The thing that is worrying me is that the flow is piping hot but the return appears cold to touch (tested at the boiler).

Please - any ideas would be welcome at this stage.

p.s. I'm quite new to this sort of thing but learning rapidly as I go along.

 

[bster]

sounds like a blockage caused by the dissolving magnetite (black rusty sludgey stuff) caused by the system cleaner, powerflush or a cold water mains flush may remove it.

 

[jingizu99]

I was afraid of that myself. At the minute though it seems that water is getting through the system albeit very slowly. The return is getting very very gradually warmer. It's been on a number of hours now and it slightly warmer than tepid. I'm wondering (what with a powerflush being an expensive process, and a mains flush sounding a little terrifying for a newbie like myself) if reintroducing a fresh amount of descaler might help to break the blockage down?

 

[Agile]

Unfortunately you have not told us the two bits of information we need.

What was the original problem?

What was the "dscaler" which you put into your system?

I may also wonder what prompted you to use the second product !

Tony

 

[pannierstan]

I think you have a huge airlock myself although the system might be sludged aswell.
Try turning the boiler of and just running the pump and remove the central cap from the shaft. Run the system for a few minutes in central heating only if possible and catch the water if any comes out.
If its airlocked it will be very quiet and the progressivly get louder until you hear a whoosh and bobs your uncle.
Try taking the pup out aswell and looking at the build up on the impellor. if its bad replace the pump and then get someone in quick smart to jetflush and reconfigure the system if necessary.

Stan

 

[ChrisR]

If you have a difficult airlock, or a flake type blockage somewhere critical, it can help if you run with the pump in backwards for a while (boiler off). Only realistic if you've just had the pump out, but you have.
And yes check that impeller.
Pump valves can block too

 

[jingizu99]

I'll have a look at that.

I left it running for about 4 hours and the radiators upstairs did eventually get piping hot, so I think the system is simply running slow rather than not running at all. It wasn't immediately obvious at first.

I've had the pump out and flushed the inside with a hose on a jet setting and it seemed to help. Pulling out the central fixing gave a really good indication that it was functioning strongly. Airlocks have been my biggest worry all along. Every time the system rattles and gurgles I go around all the rads and bleed them.

The pump was making some very slight whooshing noises earlier. I'll check if it's still doing that and get back. I'll have a look at the impeller. I'll run the system tomorrow when i get back from work and see how quickly it heats. It's possible the airlock may have cleared. If not then I guess it'll be the weekend before I can drain the system and try the pump in backwards.

Thanks for the suggestions folks!

 

[Softus]

Is the pump actually running? And I don't mean does it have a supply and is it making a noise, but is it turning?

And if it's turning, is the impeller in good condition and still attached to the motor spindle?

 

[oilman]

Is the pump actually running? And I don't mean does it have a supply and is it making a noise, but is it turning?

And if it's turning, is the impeller in good condition and still attached to the motor spindle?

..............The pump is definitely working and switching the speed on it makes a noticeable noise difference..................

 

[Softus]

..............The pump is definitely working and switching the speed on it makes a noticeable noise difference..................

Fair point - I missed that sentence, but this question still applies:

...is the impeller in good condition and still attached to the motor spindle?

 

[RigidRaider]

Silly question perhaps: are you sure all your rad valves are fully open, both ends?