Drained CH System down, and now rads are only warm

[glangri2]

Hi Oh Great Knowledgeable Ones.

I am no plumbing expert, but have moved a few few rads in my time without too much trouble. However, this time the job hasn't gone according to plan.

I have got an open system, with a cold water tank and heating expansion tank in the loft, hot water tank in one of the first floor bedrooms, and a Boiler in the kitchen.

I have had to re-route the piping of one of my rads, due to another DIY project.

The rad is on the ground floor, but is fed from above on the same loop as the bedroom radiator above it.

The rad was at the end of a loop, and installed on Isolating valves so it was simple enough to remove it. Unfortunately, I also needed to move the Isolating valves further up the pipes.

I turned off the feed to the expansion tank, and opened the isolating valves to drain the system above the valve.
4 buckets worth of water flowed out before it stopped.

Once the water had stopped flowing, I cut off the pipes and refitted the valves as required.

Then I opened the feed to the expansion tank and expected to bleed the air out of the other rads one by one to allow the system to fill up again.

The problem is that there seems to be no pressure in the system, so when I open the bleed valves on the rads hardly any air comes out.

With the heating on, the bottom 3rd of each rad warms up, but like I said, little or no air comes out when I open the bleed valves.

Help - Am I missing something simple here?

The pump seems to be working OK, and there is plenty of hot water in the tank. The pipe above the pump is nice and hot when the pump is running.

Have I introduced a nice fat air lock into the system, or could I have dislodged a lump of sludge that is now causing a blockage ?

Any advice on what to do next would be greatly appreciated.

My ears are going to start hurting if I have to go through many more bouts of the early morning moaning I was subjeted to this morning as the family got up to get ready for school, and realised how cold the house was.

Cheers
Gary

 

[Hugh Jaleak]

Is the water actually getting through from the F&E tank into the system? Common point for blockages is at the bottom of the cold feed.

 

[glangri2]

Is the water actually getting through from the F&E tank into the system? Common point for blockages is at the bottom of the cold feed.

How can I check that?
Some water has got through because the rads are warming up at the bottom, and if I open the new isolator valves water does flow through them.

Could I open one of the radiator drain cocks and just let water flow through the system for a bit to try and dislodge whatever is causing the problem?

 

[Hugh Jaleak]

I'd shut the water supply off to the F&E tank, (or tie ballvalve up, whichever easiest). Drain some water off from the system. Restore supply to F&E tank, this should start to refill as the water goes into the system, and will show if there is a blockage in the cold feed. If you have any motorised valves, make sure the lever on the side is set to Manual when refilling, and check the pump isnt airlocked. I'd recommend you dont run the system until you have ascertained there is sufficient water in there!

Running a magnet over the pipes can also show if there is a blockage, the sludge will cause a magnet to attract.

 

[JohnD]

Yes, like Hugh says.

What you are describing is very typical of a blocked feed in an open vented system, when, after you have taken a radiator off, the system does not refill properly. Look in the F&E tank, if there is mud at the bottom, bale it out and sponge it clean to avoid drawing any more sludge down.

See FAQ 12 //www.diynot.com/forums/viewtopic.php?t=175736&start=0uia

If you can't get any water flowing down the feed pipe, you will have to cut out the blocked section. Chemicals can't reach a blockage if there is no flow in the pipe. A magnet will stick to the copper pipe where there is a buildup of black iron oxide. It is usually at the "T" where the feed pipe from the F&E tank joins onto the larger circulating pipes, usually close to the pump and/or boiler. I had this once and it took me a long time to understand that it was not an airlock.

Once you manage to get some flow going down the F&E, add a litre of Sentinel X400 at the earliest opportunity (it will cost you about £15) and ensure that it is drawn down into the sytem and circulated by the pump. This loosens old sludge and sediment. You will know it is starting to work when the circulating water goes jet black with loosened sediment. After a few weeks (up to 4) of normal use, drain the system, and rinse it and use an inhibitor such as X100 in the final fill. This will bring out a lot of the loosened sediment. If you can afford an extra £100 or so, fit a Magnaclean or Spirovent which will trap remaining circulating sediment before it can build up into another blockage. I guarantee you will be delighted and amazed at the amount of sludge it collects.

X400 is a very mild cleaner, and you can safely leave it for 4 weeks, after which it starts to lose its power - it is not acidic or aggressive. There are more powerful cleaners that work faster, but they can cause unexpected damage so, as a DIYer, I recommend starting with a mild one. See FAQ20. Here is my jacket after I left it under a dripping drain cock when using DS3 acidic cleaner.

View media item 390 - - View media item 391

 

[glangri2]

Thanks for the input guys.

I'll check the feed tomorrow evening, and report back.

 

[glangri2]

Right

I checked the F&E tank, and it was clean (ish) at the bottom.

I tied up the ball cock, and then opened the drain cock on one of the down stairs rads, with the hose pipe attached and going out to the drive. I let it drain, while I went back upstairs and opened the bleed valve on the rad above the one that was draining.

After 30 seconds or so, I closed the bleed valve, went to check downstairs, closed the drain cock, checked outside and sure enough there was water all over the drive.


Back up in the loft, the F&E tank was empty.

I untied the ball cock, and then went back down stairs and opened the rad drain cock again to allow a bit of 'through flow'.

After a minute or so I closed the drain cock, and let the F&E tank finish filling up.

I tried to bleed the upstairs rads, and they all bled properly. Nice audible hiss, until water appeared.

Everything seemed to be working OK, until I checked the rads later and it seems that the Upstairs ones are OK, but the downstairs ones are cold.

I am now assuming that there was a bit of a blockage somewhere near the cold feed junction, and I have shifted enough new water through the junction to move the debris along.

Next step I guess is to go for the Anti Sludge Treatment and hope that it breaks up enough get the whole system flowing again.

Anything else I should be looking into?

Cheers
Gary

 

[Hugh Jaleak]

It seems like water is getting into the system ok, so whilst there may be some sludge in there, its not preventing the system from filling. Try shutting down the upstairs rads, see if this forces the water through into the downstairs rads. If the ground floor is fed from above then it may be the circulation is sluggish so the water will take the easiest route. (Through the upstairs rads.)

If this causes the ground floor rads to heat up ok, open the upstairs rads again gradually and see what happens. If the downstairs starts to cool off again then it may be the circulation is sluggish, check pump, and if there's an air seperator fitted (small 'can' with 3 or 4 pipes connected in the pipework before the pump) these have a tendancy to block with crud.

 

[JohnD]

give it a clean with X400, it's pretty cheap and easy, especially as you have an F&E tank. Draw at least two bucketfuls out of the drain cock, with the float tied up, before you add the chemical and stir it, so that it is well drawn down into the system.

keep an eye on the system water, if it goes black, that is old sludge and sediment being washed away.

keeping the system clean will prevent future blockages, and save a lot of future trouble and expense.

 

[glangri2]

Thanks for all the help guys. A bit more flushing through, and everything is working OK.

I'll get some X400 over the weekend, and set it to work.

 

[glangri2]

Everything seemed OK, but the new rad still didn't seem to get as hot as it should.

After leaving the X400 in for 4 weeks, I then did as much of a manual flush as I could.

I turned off all of the rads and then one by one let them run on their own for about 20 minutes each. Sure enough, they all got piping hot, so I was pretty sure that most of the sludge and any blockages had been shifted.

I totally drained the system down, refilled and drained again - the water was much cleaner second time round.

I then filled the system up again, and set to trying to balance everything

With all of the lock shields fully open all of the rads got hot apart from the new one on the lounge (I monitored the order that they heated up in) . I then closed all of the lockshields apart from the lounge one - and that rad got nice and hot, and the others cooled down.

I only had to open the lock shields about half a turn on each of the other rads to get them to heat up, and this evening it seems like everythying is staying hot as it should be.

Is it normal for lockshields to only need to be opened such a small amount on all rads apart from one ?

Cheers
Gary

 

[glangri2]

PS, I have got some X100 to go in, once I am confident I won't be draining it down again .

 

[JohnD]

Is it normal for lockshields to only need to be opened such a small amount on all rads apart from one ?

Yes, they only need to be open a fraction. All the adjustment required for balancing is within less than a turn. You may want to adjust a bit more so that all rooms heat up equally fast (or, if you have no TRVs, to the same warmth). When balancing, the flow pipe on every radiator should be "too hot to hold" and the return pipe on each should be "too hot to hold for long" as a rule of (my) thumb

Though it sounds like your "cold" radiator may have been added on after the rest of the installation, so it does not have such a good flow. This often happens if a new rad is added by taking extensions from an existing rad, and will never have good flow.

If you have isolating valves with a revolving ball inside them, the orifice in the ball is very small and will constrict flow. You can buy full-bore valves, or fit 22mm valves with 15mm reducers fitted, which have an orifice about the same size as the 15mm pipe. A gate valve is non-constricting but is much bigger and unsightly.

If you have £100 to spare and can do basic DIY plumbing, you can add a Magnaclean, and I guarantee you will be amazed and delighted at how much more black sludge it traps (you can never get it all out)

View media item 12015
View media item 12016

 

[glangri2]

The 'Cold Rad' isn't new, but it has been relocated, and you are right - I did fit isolating valves as part of moving the pipes.

That could be the whole cause of the problem - I think that I'll call in at screwfix on the way home tomorrow, and get a couple of full bore isolating Valves to fit in.

One more drain down, and I could be there.

As for the Magna clean, I have had a couple of suggestions to fit one of those, so when funds allow, I will definitely look into it ............. need to recover from the expense of Christmas first though.