Can't get my central heating to refill

[DIYnot]

Chris's Picture:

Picture 3

 

[chris547]

I tried the ChrisR approach full of hope and failed to budge the gunge using mains pressure down the Cold Feed.

I tried the softus approach and removed the connector at the Tee and physically removed the rusty gungy crap and poked a wire about.

I also tried applying mains pressure to the open end of the tee that I had cut into. Water ran out of the drain off point.
I therefore replaced the straight connector and let the F/E tank refill. It did but no water seemed to flow from it into the rads. The tank filled and shut down.


I am totally confused and demoralised. What can be happening?

 

[chris547]

I had a real epic getting that fitting off and was exhausted. I am building up a bit of respect for plumbers. Not an easy job. 2 hours it took me and I resorted to sawing it off with a hacksaw. I took great care and have not damaged the copper pipe.

Then I poked around and got some gunge out. I applied mains pressure to the open Tee end and got a flow from the drain point. Then I put on a new straight connector and recharged the F/E tank.

Not much happened and the system did not refill.

I am confused and a bit down and unsure what to try next.

Its an epic!

 

[PEDANTICVINDICTIVEMAN]

Think I would drain off, cap off the cold feed pipe and then tee the cold feed into the vent higher up, looks like the damn thing is source of trouble and will be again by the looks of the installation.

 

[meldrew's_mate]

Stick with it Chris;

You've cleared the lower blockage physically. I suggest the following:-

Go and buy a 15mm 1/4 turn isolator valve, a tank insulating jacket, and a packet of chocolate hobnobs.

Drain the F & E tank again. (At least this will be clean by now) Cut the isolator into the cold feed pipework at a convenient position, usually just at the top of the cylinder level. Now you have a convenient means of isolation.

Stop for tea & bickies.

Remove the lower section of cold feed pipe and take it outside before poking it clear. Flush it clean before bringing it anywhere near your new beige carpet.

Refit pipe, turn on and fill F & E tank.
Open isolation valve to refill.

More tea & bickies (if you bought the large pack you'll have some left)

Congratulate yourself by fitting the cylinder jacket.
OR
Collapse in a sobbing heap if it doesn't work. realising that the blockage has been pushed down the 22mm pipe. Sort this by removing the pump, opening the pump valve, and catching the gunge as it flows out. (or try less messy approach mentioned earlier)

FINALLY, treat the system to a litre of X400 sludge remover before redraining & filling with X100 inhibitor.

 

[Softus]

Honestly Chris, whilst ChrisR's idea is both pragmatic and excellent, this is the point at which I would cut my losses and get under that floor to expose as much of the 22mm pipe as you can so that you can make on a new coupling. I would use a 22mm Hep2o which is easily demountable.

Then you can run new 22mm copper (or Hep2o) to the pump inlet, with new tees, with the vent coming off lower than the cold feed. Also, replace as much of the cold feed as you can get to with either new copper or new 15mm Hep2o barrier pipe.

A tip, nay, strong recommendation, when fitting a Hep2o coupling onto copper, especially old copper that you might even have to saw...

Firstly, do NOT leave any burr on the outside of the copper. Secondly, don't risk damage to the rubber 'O' ring from any remaining sharp edge, even if there's no burr - the risk arises if you just push on the push-on fitting. This might sound crazy, but instead do this: with reasonably clean hands, disassemble the fitting, remove the 'O' ring, reassemble, push the fitting onto the copper, disassemble, and fit the 'O' ring over the copper carefully with your fingers. Then replace the body of the fitting whilst avoiding pushing the green grab ring further down the tube, and screw up the nut.

If you do this with every Hep2o fitting that's going onto copper, you will never have a leak there.

Whilst meldrew's_mate is being helpful, I doubt that the blockage will be enough to prevent flow if it's been pushed into the 22mm pipework, since it's usually very solid around the tees into the 22mm and breaks up into powder when you poke it.

(The powder is still bad for TRVs, but if you've been running an unprotected system, unknowingly or not, then all these problems have just been waiting to occur.)

 

[chris547]

Finally got the system running just before the cold snap. It was an epic and a fair amount of pipe was gunged up and had to be replaced before I got a flow out of the F/E tank when I drained off some water.

I reasoned that the problem lay between the F/E tank and the drain off point so just kept replacing sections of pipe until water started to flow.

Had to replace most of the cold feed, unblock the drain off point and some of the 22mm pipe leading to the radiator that has the drain off point.

Reversed the cold feed and vent so that now the cold water feed is next to the pump inlet.

Filled up, bled the system, drained off some water with the cold feed off, emptied the F/E tank, added corrosion inhibitor, switched on the cold feed and all seems hunky dory. System running quietly and all rads hot to the top. Hot water fine and the HWC insulation replaced.

Only thing confusing me is the bypass of the MZ valve from the pump to the heating circuit. See picture 3. Is this meant to be open, closed or half open? Why is this fitted?

Thanks to everyone who gave me support. My respect for plumbers has grown. Not an easy job and physically demanding!

chris547

 

[Softus]

Only thing confusing me is the bypass of the MZ valve from the pump to the heating circuit. See picture 3. Is this meant to be open, closed or half open? Why is this fitted?
chris547

You've done well there Chris, and you'll reap the rewards of your hard work for years to come.

Regarding the bypass, I'm feeling a bit lazy so haven't refreshed my memory of your system, but it may be necessary or it may just be a legacy. Since other pipework was wrong it might even be a white elephant. Generally though, the bypass allows passage of heat away from the boiler when every other valve is shut - this avoids hot spots inside the boiler that would otherwise risk damaging it (or shortening its life).

So, I always close the bypass, then open it until water is only just flowing. Half to one turn of a gate valve should do it, but remember with gate valves that they invariably have a lot of hysteresis and therefore feel very easy to turn before the valve begins to open.

 

[chris547]

Thanks Softus you have been very supportive and encouraging

Bypass probably is no longer required as the towel rail can always draw water but I will leave it open a peep as you suggest


Chris

 

[Softus]

All the best