Problem with a central heating type 21 radiator

barnaclebill

I have.  a type 21 central heating boiler in my large lounge, it  has been cooler than the others in the house for some time and I suspected sludge build up so today I drained it, not much black residue except at the very end.

First puzzle, it drained very slowly at the inlet even with the air bleed full open so I started to drain at the outlet which drained at a normal rate. removed it to the garden with help and we flushed it a number of times by hose. We then tried the valves and noted the flow from the temp control valve on the inlet side was weak. After refitting tried filling from the inlet with outlet closed and one air bleed open but it was too slow and had to fill from the outlet valve, started the boiler taking care to keep the pressure in the system and fully bleed the rad.

All the other rads warmed up quickly but this one stayed cold, tonight it is still cold the inlet pipe is hot as it enters but the rad is cold which is worse than before, I have removed the control head from the valve and the plunger can be pushed down and it springs back so I believe the valve has some restriction but am still puzzled as to why it was so slow to drain at the inlet side making me think there may be some problem there also. Any ideas, one other thing it looks like this has been fitted after the other rads as it has plastic pipes in and out, all the others are copper, the house is 60 years old

Bendy_House

The 'lockshield' valve and the 'control' (TRV in your case) valve should both have an easy free flow through them when opened fully.

The TRV seems to be working, in that the pin presses down easily, and pops back up freely. That's not to say it doesn't have a blockage, of course, or the rubber valve seal has not detached from the pin. The obvious thing to do is to replace it, like-for-like so hopefully an easy task. Something is amiss if it drains only slowly, so really you shouldn't be pondering any further until you've discounted this as the issue first.

When flushing out a rad with a hose, it really needs constant bashing with something like a rubber mallet covered in cloth (to protect the paint), mainly along the rad bottom/middle area. Watch the water flow - if more 'black' starts to appear when you thump, then keep on thumping.

If you don't already have one, fit a magnetic filter on the return pipe to the boiler, and add a dose of 'filter-aid' to this - long-term cleaner you can leave in your system.

HHarry

You might have an air lock or partial blockage in that pipe.  You could try turn8ng off the valves to the other radiators and see if the increased flow will shift it.

barnaclebill

Changed the TRV valve but no change and the old TRV is ok, main suspect is the pipe now but how to get access is next problem.

plumb1_2

As Harry said, turn off all other rads, as the heating pump might push a partial blockage through 
If not recommend a powerflush 

Bendy_House

Hi BB.

Are you up for a DIY solution?! I currently have this set up in my house, after having had repeated issues with P2P exchangers blocking up. I had a Magnaclean Pro fitted, and a dose of 'filter aid', but that didn't seem to catch everything, so I bought a proper Magnacleanse kit on t'Bay, and should be able to resell it for the same amount when I'm done with it. In theory, this 'solution' shouldn't cost more than the cleaning chemicals used.

First find a location for a Mag Filter, like the Adey - you should really have a filter fitted permanently anyway. If you want, you can just try the job with this alone - add at least one dose of X800 cleaner, and run your CH as normal. If you do as recommended by others above, and shut off (partially if not fully) most of the other rads, you'll be forcing most of the flow and cleaner through this dodgy rad and pipework.

Keep examining the filter, on a daily basis to begin with. That'll quickly tell you if you have sludge...

And if you fancy a more thorough job, get a 2nd-hand Mangacleanse on t'Bay and fit that temporarily instead - it'll go on the same fixings. With 2 much larger magnets, it catches a lot more.

Keep it going until the amount being caught starts to obviously fall off, or until the rad starts to work properly. Then you can decide to either keep it going, or to replace the permanent filter. Either way, after, say, 4 weeks, you should drain and flush through your system to remove the strong cleaner. Then add inhibitor and a filter aid - long-term cleaner.

plumb1_2

Magma cleanse or ok but no good enough to really clean/unblock the system. As it relies on the boiler pump to move any blockage and only in one direction.
I use a Kamco powerflush and connect a magnacleanse to it before connecting to boiler or heating circuit.
With the kamco you can switch direction of the flow, thus attacking any blockage on 2 sides
Plus you need to use a rad hammer in conjunction when flushing.
To do a flush is a min of 6 hrs work

barnaclebill

Fixed it this morning, sealed the radiator withe the vacuum method, closed both valves and depressurised from the bleed valve then closed it, unscrewed the inlet connection catching the small amount of water and sealed it with the old trv then opened the new trv into a container, slow flow so started banging on the pipe, water became black so kept going finally got a spurt of black grit and then a good flow. reconnected and heating back on.

When I get a new boiler next year will make sure good power flush and magfilter. Thanks for all the replies

plumb1_2

barnaclebill said:

Fixed it this morning, sealed the radiator withe the vacuum method, closed both valves and depressurised from the bleed valve then closed it, unscrewed the inlet connection catching the small amount of water and sealed it with the old trv then opened the new trv into a container, slow flow so started banging on the pipe, water became black so kept going finally got a spurt of black grit and then a good flow. reconnected and heating back on.

When I get a new boiler next year will make sure good power flush and magfilter. Thanks for all the replies

That’s great news, but make sure when you have a new boiler it’s properly powerflushed.
Most heating engineers will just put some cleaner in the new filter then drain and refill it.
Waste of time IMO, pay the extra £300 for a proper flush.

As you have found out your system is full of crap, quite a few manufacturers will now take a sample of your water in heating circuits, if a divert or or hx fails under warranty and won’t do a free fix if crap in the system. Bang goes your 7yrs warranty 

Bendy_House

Well done!

As said above, this sludge will damage modern boilers as they tend to have small and narrow waterways - a fraction of the size of that blocked pipe! So if you don't have it thoroughly flushed, expect medium-to-long term problems.

Any chance you could fit a filter now - a Magnaclean, Fernox, Sentinel, whatevs - and set it cleaning your system over the coming year by adding inhibitor/filter aid?

The presence of black sludge suggest that there's no inhibitor in the system water, so fair chance that sludge build-up will increase - ie your rads are rusting from within...

That ain't going to stop until you stop it.