Central Heating not Working

[davenich]

I have a central heating system with apparently no flow. The plumber has spent two full days working on it. All components, pump, 3-way valve. room thermostat. boiler controls are all working. The system was checked out for air locks with new vents even installed to facilitate bleeding. The system has been flushed out with flushing pump descaler replaced with inhibitor (during flushing boiler fired up & system worked). Back on normal CH pump system packed up after a day. Has it become airlocked? Is there a problem with the pump? Can any one give me advice before I recall the plumber next week.
Cheers.

 

[kevplumb]

try bleeding the pump

 

[nicho75]

The Grundfos Pump manual shows the correct fittings for these pumps if fitted upside down they can give rise to air locks.Check out your type of pump maybe its upside down as mine is.

 

[davenich]

kevplumb/nicho75
Thank you both for the advice I'll get the plumber onto it. You definitely think it's a pump problem??

 

[davenich]

Pump checked out as OK. Any ideas? Given that it all worked on the powerflush should we try a more powerful pump? I am not a plumber hence why I have to hire one, I am technically minded, but this has got both of us totally stumped. Any help please??!!

 

[kevplumb]

did you remove the pump to powerflush if so did it go back the right way?

 

[davenich]

Thanks kevplumb. Yeah we tried that even with the pump both ways round. Plumber reckons we need to put in a more powerful pump. I am concened about this since system worked before. My intuition (for what it's worth with plumbing matters!!!) tells me there is a blockage or restriction somewhere in the system. However all worked on powerflush. I'm still stumped, got to be fixable, cold mornings now kicking in.
Any more thoughts??
Cheers

 

[brumylad]

Set the system to heating only if that is possible. turn all the radiator valves off except the ones on the rad closest to the pump. If that rad then gets hot open the next one along and so on. If the first one fails to warm there must surely be a pump failure.

 

[kevplumb]

impeller fell off just cos the motors running dont mean its doing anything

 

[topgazza]

I've got the same problem Dave. My plumber replaced the pump, twice. Turned off all rads downstairs and upstairs gradually got hot, reversed the process and downstairs got hot. Turned them all on and only the nearest to pump gets hot. When he removes the screw at the front of the pump it hisses for a couple of secs everytime he powers the system off and on. The pump starts quiet but gets noisy after 3 or 4 minutes. He reckons poor flow caused by gas build up. He's coming Friday to flush and treat as apparently this hasn't been done since install, 23 years!!!!!

There is no air escaping from any of the rads, probably due to poor pressure anyway, the bleed valve near the pump will hiss for about 1 second and then water comes out. The water he has drained from the pump inlet/outlet when he removed it looks slightly rusty, slightly and there was a small amount of dispersed sludge. Its all down to good circulation I guess but in a simple vented standard system he was getting exasperated at the time it was taking NOT to cure it. He's a good guy and I have confidence and I will post the results.

 

[topgazza]

Ok, yesterday the plumber powerflushed the system reloaded anti-knock and inhibitor. Still the same problem. he tried everything. The system avtually worked OK with the powerflush attached, in effect a closed system, but one returned to its vented state no circulation.

Now I may well get some of the technicalities mixed up here but this is what happened. He was looking at the original diagrams and was explaining that he believes that it has someting to do with the relationship with the pipework between the cold feed, vent and the pump. It looked like it was trying to suck air in and he drew a diagram showing how it should be. Not a lot of work to redo the pipes about a morning but he was absolutely convinced that 20 years ago they plumbed the pump/vent/feed pipes as per the diagram for the boiler which is not ideal.

The pump would be quiet then get noisy. He had tried all sorts of things to push any air out but it kept "reappearing"As he was talking and about to show me how noisy the pump was a gurgle came from the vent pipe and the pump did not make a noise. The rads were boiling hot within 10 mintues and stayed that way.

He could only think that the chemicals had settled in the system as the boiler was now silent as well, no gentle knocking. Or the air had finally been pushed out. Honest enough to say it was good luck and to monitor it when the system had been off then on. Hopefully with all air out the resistence for the pump was fixed. Until the next time something was removed and air got in. If this happens I will get him to do the pipes as what he said made absolute sense. This sort of problem seems impossibly difficult in what is just a circle of pipes but a good guy who knows his theory, and mine did, can struggle. I'm guessing but apart from leaks causing problems bad pipework in general , dips and bends in inappropriate places can cause these difficult problems. I'll now if its still working later today when my wife goes there....

 

[davenich]

Thanks Gazza. I've been working away so I am no further on with my system. You're experiences bear out my own views that somehow, due to the system configuration, it is entraining air. I am going to do what you did with the plumber sketch out the system and get back to basics on the hydraulics of the system. The plumber's a cracking bloke very experienced who knows his stuff. Hopefully between us we'll get to the bottom of it. I am conviced that putting in a bigger pump will make it worse. The static head on the system from the header tank is quite low at one point and this could be the problem point. As you allude to 'the devil's in the detail' and with a lot of things its an art as much as a science.
Cheers

 

[topgazza]

Support the bigger pump theory.When the pump in situ was turned to max revs it got noisier, the sound of gurgling/air, and bled more air from the center screw. Has to create more vortex in the system, hence more air. The odd thing is how long the system worked, 20 years, without a problem. I suspect that in my case the flush helped as it had never been done in that time. The potential for the problem is still there with the pipework though.

 

[croydoncorgi]

Systems that are difficult to refill are a b****r!
But if you had the powerflush pump in place of the regular one and it was powerful enough to shift out the air, did you actually try swapping the usual pump back in and opening up the vent, etc., without draining the system? Once the air's out, the pro0blem should be gone.

 

[topgazza]

He did but everytime he started the system it would still not shift any water through. The pump would make a noise and you could bleed very very small amounts of air from the bleed valve and the pump. It looked like fresh amounts of air were being generated in the system. Also this lack of "balance" with the design of the return/pump/vent seemed to make it worse. Once the system appeared to be clear all seemed well so maybe ANY gas in this system with the design will cause this issue. Maybe clearing all the filth out of the system with possible hydrogen gas being produced did the job. As I said with a closed powerflush all worked fine but revert back to the vent and it all ground to a halt. He got there in the end