CH crisis no flow

[Animal]

Old system, looks 1970s, but with modern boiler & magnetic filter. Symptoms are kettling & very rapid temp rise when the burner comes on, rads are cold. Looks like no flow. I wish I'd checked how far the heated water moved but didn't. The filter was clogged, but cleaning it didn't solve the no flow.

Figured the pump was most likely clogged, but can't undo either of its big fixing nuts. OK, try separating the 2 halves of the casting - turns out they're cemented together with something hard & haven't been able to get any way to separate them. Can't put a lot of force on it as the pump is mounted on the copper piping, and I've not been able to remove it so far.

Ended up needing to access the header tank & found it badly fouled with corrosion junk & biojunk.Cleaned it but don't know what chemical to use to prevent the bio returning. System could also use some strong cleaner, one rad has lousy flow, again not sure what to choose.

Primary circuit was as clear as tapwater, presumably no chemical in it. Turns out the header has overflowed at times. Ball is almost completely under the water surface, the valve closes fully if the ball is lifted by hand. Not sure if it's a stiff valve or a leaky ball.

Suggestions appreciated, it needs fixing quickly. Thanks

[Roger Mills]

The pump would be my first port of call. Is there a cap you can remove to check that the shaft is rotating? If it *is* rotating but there's still no flow, it's possible that the impeller has become detached from the shaft. You really need to remove the pump to check it. You need two long-handled stillsons - one on each side and, preferably a helper. A bit of persuasion with a copper hammer on the ends of the stillsons may be needed.

With regard to the F&E tank overflowing - is the water level in the main cold water header tank higher than that in the F&E tank? If so, it's possible that the coil in the hot water cylinder is leaking and allowing secondary water to get into the primary system. This can be checked by turning off the mains feed to the F&E tank, and seeing whether the level

*still* rises.

[John Rumm]

Pump sounds like a likely culprit. Check it is getting power. Can you take the silver screw out the middle and see if the shaft turns with a screwdriver?

[Animal]

The pump nuts wouldn't undo, but got it off with pipes attached. Split it open, impellor is completely clean. It gets power, will check it rotates tomorrow.

It only overflowed on occasion - that has been solved, now know the ball float is a ball sink. New balls will be attached tomorrow.

There's still no flow. System has been filled with water & bleach to sit overnight. If the clog is bio that might dissolve it. If not, mains pressure flushing section by section looks like the next plan. Hatefully time consuming but not sure there's another option. The valve is a single 3 way, so its failure would not cause the no primary flow symptoms happening.

Thanks everyone.

[Brian Gaff]

If its an old ballcock, replace it in any case. I ended up duct taping a couple of empty plastic butter dishes to one as a quick fix to stop the overflow some years ago. Some systems also seem to get through pumps like as if they were made of cheese. No real idea why. Brian

[R D S]

When it tries to fire is there a drop or rise on the pressure gauge? That would, I think, suggest the pump is OK

Our recent problem was as you describe and it turned out there was a lot of crap from oxidisation in the heat exchanger.

[Tim+]

It has a header tank so there’s unlikely to be a pressure gauge!

Sounds like a dead/dying pump or some other system blockage, but my money is on the pump.

Tim

[Andrew]

If your header ballcock is not shutting off then you should have noticed the overflow. At this time of year a dribbling overflow will freeze and then the tank overflows with disastrous results.

Even if this does not happen you are introducing fresh oxygenated water into the system which is also a very BAD thing.

It sounds like you have never taken a look at the header tank for a long time. Your system probably needs a drain down, the run with a flushing cleaner compound for a week then forcibly flushed out with a hosepipe and refilled with fresh anti-corrosion inhibitor. And fix the header tank ballcock.

Not something to be undertaken at this time of year though.

[Animal]

Open system, no pressure gauge.

The pump spins, whether it's going as fast as it should I've no clue. The impellor moves freely. Pump leds indicate max speed.

Just one lump of the junk in the header would block the system, and there must have been a kilo or so of it. My bet is on junk in the system.

A day with bleach has resulted in flow, but not enough. 3 rads don't heat up, and the boiler short cycles & cuts out after a few minutes with code F23... 'Water shortage, temperature difference between flow and return NTC too large. Pump blocked or defective, pump output too low, flow and return NTC interchan-ged.' It slowly heated the primary return to 40C after many resets, 1 or 2C rise each time. So it needs a cleanout.

There's a problem with power flushing: a fair bit of the pipework I don't know where it runs or what's connected where, and it's very inaccessible. Sludge in the rads is a minor issue, blocked pipes look like the problem. Some sort of plunger to use vigorously while draining could help, but can't think how to set that up.

Planning to use citric acid next. Hesitant to use sodium hydrogen sulphate, not sure if it would do damage. Could also try X800, but makes sense to try the other options first.

Oh! I am dense. I think I know why it's cutting out!

Re the ball, I tied it up by its unhealthy ball for now. Safer than leaving open header systems to self fill anyway. BBS

[John Rumm]

If you do mains flushing - basically inject water in somewhere, and connect somewhere else to the drain - you can remove one rad and make connections to the tails, then you can get quite good results if you turn off all rads but one. Let that have full flow for a few mins, then open the next, and turn off the one you just completed - work round until all have been done. Cap the feed and expansion while flushing. Then you can turn off all the rads, and flush up into the F&E by capping the F&E connection and the vent in alternation. (you will need someone at the tap end on the end of the phone since you don't want to overflow the tank!)

[Animal]

Sounds a good next step if chems don't do it, and I'm not confident they will. I just hope the plastic filter never sees mains pressure or it'll pop. Hopefully there isn't a blockage that hard somewhere.

[Harry Bloomfield Esq]

Open vented, so there will be no gauge.

[Animal]

Some leaks fixed. Ball surgery performed. Pump makes graunching noises so will replace. Otherwise I think some of the system will work, cleaning hopefully fix the rest.