My resolved problems with central heating and hot water

[MrInteractive]

I have a y plan open vent system as below

And I had the following symptoms initially for a period of months which gradually got worse
1) The central heating would occasionally not work
2) Banging on the valve would often cause it to start working, accompanied by some gurgling sounds
3) When the boiler started up there would often be gurgling sounds from the hot water tank
4) The Honeywell motorised 3 way valve appeared not be working properly: there is a switch at the bottom one could move and according to youtube videos it should offer resistance and then return to its original position due to a powerful spring. My lever seemed to offer no resistance and did not return to its original position.
5) The pump seemed to fine as the the throbbing of the pipes nearby seemed to indicate water flow
6) Radiators downstairs would not work, but those upstairs would

Later symptoms
1) The central heating and the hot water stopped working
2) The throbbing of the pipes near the pump seemed somewhat less than before when things were vaguely working, and the pump noise now seemed very smooth and quiet.
3) The boiler on start up would fire up for a few seconds, bubble and then stop, which would warm the pipework from the boiler for a few feet.
4) The pipe on the outflow from the pump would be warm, but the pipe on the input side of the pump from the boiler to the pump was cool.
5) On inspection of the pump by unscrewing the octagonal knob showed it was rotating.

On investigating by removing pump
1) There was no water in the feed to the pump
So the pump had been dry and the heat in the outlet pipe of the pump was generated purely from the pipe's motor.

When I had inspected the pump as I described above to see if it was rotating by unscrewing of the octagonal knob I had not checked for water by bending the knob to one side as per the instructions I found online.

The fact there was no water meant the feed from the expansion tank was not working. I investigated the section of piping above the valve and removed it, it had problems but not with the original problem, so that left the pipework next to the tee piece as the blocked section, which was confirmed when I tried to stick a rod into the pipe section below the valve above the tee to the pipe just above the pump.

So, I attempted to desolder the tee piece from the air separator to see what was going on but couldn't persuade the two fittings to part company. After fruitless days of effort I then sawed the connecting pipework, whereupon I discovered the reason for my problems: a very hard and huge magnetite weld had formed across the pipework between the two that almost completely blocked it. I include a picture in the diagram below which includes all of my investigations.

Replacing the tee piece and the air separator and resoldering all the associated joints fixed the problem. When I was purchasing the new air separator and tee piece I met a gas engineer who said the air separators were a bad idea and that these days plumbers remove them and join the vent to the feed just above the tee piece in my diagram and eliminate the separator completely. I considered implementing his suggestion but in the end doing the five soldering tasks I had to do was difficult enough for someone who hadn't done it before.

What I learnt
1) Check for water in the pump
2) Don't assume a pump making a noise or vibrating is pumping
3) When both the central heating and the hot water fail, then the Honeywell motorised valve cannot be the problem as it can only turn off one of the systems not both.
4) Don't ignore gurgling noises, something is blocked
5) Bashing a valve can clearly transmit vibration along the pipe, and in my case released some blockage in the pipework near the air separator to allow the water feed from the feed tank to clear to some degree.
6) Don't assume pipes get hot because of hot water in them, pump motors can make pipes hot too.
7) If the pipework from the boiler is hot, then towards the pump cold and then after the pump hot, then something is going badly wrong.
8) If the boiler starts up for a few seconds and stops, it probably doesn't have water being pumped through it.
9) Don't assume that just solder is holding a pipe together and don't get exasperated after numerous attempts to desolder with a blowtorch.
10) Be careful to check that one is using FULL extension of the lever in a Honeywell v4073a1039 valve even if you can't see it! The resistance it offers is very high and there seems to be more play in the lever in an old valve than appears to be in a new valve, which I tested in a plumber's supply shop. My valve appears to be fine.
11) and more that I have forgotten no doubt

 

[FiremanT]

Blimey.

Searching through posts and asking a few questions would probably have been quicker and easier.

Some guys do say air separators cause problems, but I fitted loads,and never had any issues. But my swaps were always clean (apart from in the v early days when some would not pay for a chem cleanse. Eventually I stopped it being optional). I cannot recall being called back to a sludged system I fitted, although one can never now if they called someone else.

 

[MrInteractive]

I did ask lots of questions in my initial thread
https://www.diynot.com/diy/threads/how-to-flush-a-heating-system-with-mains-water.38902/
which started off mostly with questions about the Honeywell diverter valve, and then mostly how a pump can be rotating yet not pumping, but the answers were mostly of the form

1) Get a man in
2) You haven't detailed the whole system ( which as I predicted had nothing to do with the issue )
3) Get a man in
4) I had one of those valves go wrong once
5) I said get a man in!
6) You have typed too much
7) How many more times I have told you to stop messing about and get a man in
8) It might be the pump
9) Look, you keep on ignoring the advice to get a man in
and when I established the pump had no water, I finally got a useful bit of advice to look at the expansion tank feed and replace the pipe.

 

[MrInteractive]

Would you recommend cleansing the system with an Fernox F3 cleaning solution ?

Would you attempt a mains powered-flush?