Poor water flow but pump and 3-way seem fine

[cambsukguy]

How much force should the impeller have? Does my system use only this pump?

After reading a substantial number of articles, the story is as follows:

System: Grundfos 10-50 pump drawing water from Netaheat 10/16 boiler, 1988. 3-way valve afterward feed heating coil and CH circuit. Microbore pipes to rads.

Rads never seem to have had cold spots, the system has had inhibitor and has been looked after reasonably well.

For some time boiler (netaheat 10/16 c. 1988) has cycled on/off when heat was in demand. Mostly ignored because the house was warm enough and hot water was fine. Boiler outlet pipe gets very hot no problem.

Finally checking why some rads were just luke warm necessitated hasty gate valve replacement because the old ones leaked when actually utilised!

Pump impeller seemed to rotating at all 3 settings.

3-way valve controller is removed to have manual control of HW/CH flow. Internally checked to ensure flow is ok.

Drained system through kitchen rad and left it for a while. F&E tank seemed fine because water was in continual supply (30 or 40 mins of flushing).

Refitted pump and refilled, along with anti-sludge chemical, bled rads. No improvement.

Separated pump housing in-situ and found impeller completely blocked with detritus. Cleaned completely and really assumed the lack of pressure would be fixed. I also checked the 'torque' of the impeller; It took reasonable pressure (with a towel-in-hand) to stop it on position 1. Position 3 was pretty forceful, bring to mind a disc brake. it could be stopped but really felt like it was enough to do the job.

It did not fix the system problem though. I will buy a pump if it were the pump but the force seemed ample and the impeller seems fine. It is a solid metal affair with surprisingly small impeller width (5 mm max). The flow enters the centre and is impelled outward. I did notice that the impeller moves on its spindle more than i would expect; might this take it away from the 'input' water supply and reduce the flow pressure? There is no sign of a 'tight' fit mechansm to ensure that no flow goes around the impeller. Is there a part missing that has disintegrated perhaps?

Now, the rads upstairs grudgingly get warm, even hot eventually, like before. The boiler still cycles. Only one downstairs rad finally heated to warm, others are stone cold. All were bled of air. I tried bleeding a radiator downstairs with one side valve off and bleeding a lot of liquid (because I read it in one of these articles). I expected hot water, eventually. After more than a litre I stopped and swapped to the other valve.

This is the interesting part; the water stopped! No flow at all after half a litre or so. Does this mean I have a air block between the upstairs and the downstairs? The system has been drained a few times in the past without this problem occurring. I repeat, the F&E tank still had water in it after flushing and the upsatirs rads did not drain to the downstairs bleed valve.

I think some pump flow occurs, the boiler water arrives faster than convection would seem to allow allow. However, the water flows into the hot tank (air screw also bled at that point). The outflow takes some time to heat even if the pump is on 3.


So, finally, any ideas or just replaced the pump and hope?

cheers, Ivan

 

[waterworks]

Central heating pump as it is always called is actually not a pump as such, it's real title is a Circulator so when blockages of air/debris etc stop the flow the circulator has a job to move it.

 

[cambsukguy]

yes, it is a more accurate name to be sure; bit longer to type! My main problem is that it seems to be operate but doesn't 'push' hard enough perhaps. One of my many questions was whether the impeller lateral movement might be a problem and/or the torque of the motor itself.

 

[MANDATE]

Did you have the 3 way valve manually set in mid position when re- filling?

 

[cambsukguy]

not sure about the position at actual filling time but i subsequently put it mid-posn to test the flows. I bled the air off the top of the HW feed so i know water went in there ok and i felt heat along the radiator feed pipe too. it just seems to take a while, if ever, to reach the rads and takes a while to exit the hot tank coil warm too. I assume heat transfer cannot be that efficient especially at pump posn 3 so i expected hot water to come out of the HW tank exit fairly quickly.

 

[andytheplumber]

Sounds like it needs a powerflush, and possibly a new pump. And then proper balancing

 

[cambsukguy]

well, the system always worked, after a fashion, pretty much regardless of settings, heat moved around, doors were open etc. The upstairs tended to be shut down more simply because heat rises.

What I will do is shut down all the rads upstairs and see if the downstairs will get warm; at least after I drain and refill it again to remove the sludge chemical, try to clear the air pocket maybe and replace a leaking rad valve collar that refuses to tighten (I stopped the actual leak by shutting down the valve on that side). Lots of my valves seemed to have been very poorly fitted; they leaked for years simply because I had the temerity to turn them. I ended up tightening the collars down which I assumed the original guy had failed to do; perhaps the same guy that left 7 gas leaks in the house and made british gas shut our supply off until a corgi plumber gave them a certifcate saying it was fixed.

The fact that the downstairs rad simply stopped bleeding water is s mystery.

I cannot do anything for quite a while because I had to leave home for some time and won't get a chance to do anything. This is all by way of getting any info I can to attack the problem when I do get home.

I appreciate any and all input. Still leaning toward simply fitting a new pump; if it fails I will just accept the cost and have a spare and the knowledge that it isn't the pump for sure.

 

[andytheplumber]

if the down stairs rad is not filling up it sounds like its blocked or air locked.

 

[MANDATE]

I can't really see how a 'air lock' can prevent water coming out of a bleed valve. If there's a head of water in the tank to give pressure and the bleed valve is not blocked, then there's nothing to stop it. An air bubble will move as long as there is a pressure difference.
To me it sounds more like a sediment blockage. one valve is closed off and the other although open indicates a blockage in that area.
Could be the entrance to the radiator or below the valve.
Best thing in my opinion would be to close valves and remove radiator.
With radiator removed attach hose to each valve it turn and run off a good bucketful of water off each side. This will release any air lock and/or identify if there is a blockage just below any of the valves.
I always do this before refitting a radiator.

 

[cambsukguy]

Yes, although that particular radiator, a small one in the downstairs toilet, had always been ok. Since I have to remove a rad upstairs because the valve leaks if opened and the collar is jammed beyond moving, I am interested to look at the condition within generally and do them all if it appears bad enough to warrant it.

After I drain the system and check again after refilling I will do what you suggest for each radiator downstairs which fails to drain continuously.

I did originally drain the system via the kitchen rad and it ran clean for 30 mins. This rad still doesn't get warm though it did previously so there is a problem over and beyond the extra one I have now, such as the pump.

 

[MANDATE]

Looked at a problem couple of weeks back. 1 radiator cold. 1 just warm and others seemed ok.
The cold radiator was removed and examined and cleaned. Water run off from each side and radiator replaced and it made no difference.
Examined pipe work and found by pass valve too far open. Closed this more and cold radiator gets warm.
Decision made to remove pump and found inlet and outlet partially blocked, down to 3 or 4mm. Pump also found to have faulty bearing so pump and pump isolating valves replaced.
If you have a blockage, it all depends where it is as to what it affects.
A blockage in the flow or return pipe does not prevent draining down.
Don't be convinced everything is ok because the water runs clear when flushing. The flow pipe becomes the return pipe at the last radiator in the circuit and you may have two or more circuits.
So there's at least two routes the water could take to get to the drain off point and if there is a blockage it will be by passed.

 

[cambsukguy]

I had go when I got home this week; drained the cleaner out of the system at all four drain poins on the ground floor. Close off the top floor radiators.

I removed one upstairs because the valve leaks unless closed but realised it is 8mm pipwork not 10mm and i had only one (10mm) reducer from the new 15mm valve I bought. The rad was really clean, small amounts of black water only.

I fired up the boiler and refilled the system using one side of each downstairs rad and then the other in turn; all filled (with hot water) ok both ways. I presume the boiler water was drained into them. They were cooler at the bottom where the rads used more water than a boiler-load.

Since the radiators then all started to get cold and the boiler kept shutting off, I removed the pump and put it in a bucket of water. This is my real problem; it obviously pumps, seemingly well at all speeds. Speed 1 pushes water around the bucket and up the side a little when at an angle. Position 3 tended to push a lot; almost over the side but pulsed, perhaps drawing in air at one side because it reduced the water level.

Is this the correct pump pressure or it is a pitiful shadow of its former self?

The only other explanation it seems is that the boiler has some kind of blockage in it. I saw a drain cock on one side that seems to get no mention in the installation manual so I presume it was put there by the installer. I attached a hose and opened it and there is virtually no flow.

Does anyone know what this is for? (apart from the obvious; it is a drain cock and the boiler pipe is block somehow). Bearing in mind the boiler water drains into rads, obviously there is one way out at least.

So, if I can confirm the drain cock is supposed to flow fully and is therefore blocked; I will ask an expert to fix it for me. If I can confirm the pump is supposed to wet the ceiling when it is on in a bucket, I will get a new pump.

As an aside (perhaps) the rads are all open and bled and the upstairs ones are warmish, the closest to the boiler is warmest also; presumably convection and/or pitiful flow. Downstairs all cold still.

Thanks to anyone still hanging in there.

 

[cambsukguy]

So, I put in a new pump. No change, which shows I should have believed my own eyes.

I worked out why the boiler wouldn't drain; the plug was blocked with crud. Fell out at the merest suggestion of a sharp poke. I drained it for 10 minutes or so but it was not help either.

I now presume the boiler is faulty in some way I do not know; perhaps there is a valve inside it or even a filter.

Nothing in the manual but I will call someone and hope they can discover the problem.

 

[stardanny]

Sound like a airlock or part blocked on boiler return pipe. Try turn off all radiator valve off ( only on wheelvalve per radiators) but the one ( downstair rad if you want, and see what happen. Or try turn heating off and switch hot water on only, the water should get hot on return pipe to boiler ( only when the hot water is cool in cylinder.) if not, airlock or part blocked on return pipe to boiler.

As it a mircobore system, it may be that the pipes may have narrow up thus reducing flow.

Dan.

 

[cambsukguy]

The hot water doesn't get hot, the pipes get hot (if you wait long enough) by convenction it seems. I turned off all radiators and water still doesn't get hot. The radiator feed pipes get warm eventually too.

The boiler return gets hot eventually (presumably also by convection).

If it is a blockage (possible for sure) then several system refills didn't fix it.

Basically, there is no flow - the pipes to the boiler and HW are 22mm, I am sure they are not blocked.

I will post any resolution here if I can get someone to fix it eventually.