Cold Rads. New Pump?

[GeoffH]

Last year I drained my system, flushed it and fitted TRVs and new lockshields. All has been fine for a while (after eventually getting all the air out of the system). I did not bother trying to balance the rads, as they all got hot. However, after being away last weekend (leaving CH on), I returned home to find that the downstairs rads were not getting warm.

Last night I closed off all rads up and down, and opened up each downstairs rad in turn, one at a time. Each one got hot. If I try to get all downstairs rads open, with lockshields in various positions, some get slightly warm, some are cold. The pump is turning.(Opened centre screw and shaft is turning)

Question: do I now have a balancing problem or a pump problem? Pump is a Grundfos (model no. not to hand at the moment) running at fastest speed.

TIA

Geoff

 

[peter anderson]

well you can easily balance them yourself so maybe its best to try that first (seeing as you should do that anyway). You can buy a couple of clip on thermometers from a plumbers merchant or you can do it without them

Do you know how to balance your radiators?

I'll tell you if you dont know

 

[GeoffH]

Peter, I'm just curious as to why I didn't need to do any balancing previously, which makes me suspect the pump. Not sure if pump is fully working; i.e. it is rotating but who knows?

I have read up on balancing today and the three ways seem to be:
1) Use thermometers to get the ~11 deg C difference.
2) Start at the rad furthest away from the pump and open lockshield fully. Next rad, close lockshield " a bit".
3) Start with rad nearest to pump, open lockshield slightly. Go to next rad, open lockshield "a bit more".

What is you preferred method? Should this be done with all upstairs rads fully off and then re-checked with them opened up slightly?

Geoff

 

[peter anderson]

Geoff,

I'm not a heating engineer just a plumbing student.

If your upstairs radiators are warm enough but not overhot and your downstairs radiators are too cool then I guess the problem isn't that your system needs balancing.

I'm assuming that a) your boiler is at the right temperature on the boiler thermostat b) your room thermostat is at the right temperature 3)TRVs are not set too low b) your pump is on 3 if it is running at the fastest speed.

Which radiators are closest to the boiler? upstairs or downstairs? If the downstairs are furthest from the boiler then it makes sense that if the pump is faulty then they should be coolest and the upstairs radiators not overhot. The radiators that are too cool, are they cool all over or just at the top or bottom or middle?

Possible problems could be that the pump is faulty, the boiler thermostat is faulty, the boiler is faulty.

If you're interested here is a way to balance the radiators without thermometers. But if no radiators are too hot then it won't help you.





trial and error method by John Reginald, author of "central heating"

1)Turn on the central heating and whilst it is warming up (if it isnt already on)

2)Open all radiator valves with control heads (including TRVs) to maximum

3)At the hottest radiator remove the cap on the lockshield valve

4) Turn the spindle clockwise one quarter of a turn using an adjustable spanner

5)Wait for 20 mins

6) check the effect on this radiator and other radiators

7) If the radiator is still hottest turn one quarter of a turn again

8) Wait for 20 minutes

9) Repeat steps 4-6 until no longer hottest

10) Repeat 3-9 with other hot radiators until they are all delivering the required temperature for each room

 

[GeoffH]

Thanks Peter, I'll give it a go now I am home.

Everything else seems ok, but maby I've missed something that has changed over the weekend. I will double check and then try to balance the rads.

Rads are either cold all over or hot all over(if turned on on their own)

Thanks for your help so far.

Geoff

P.S. What is the purpose of the central screw in a pump? Is it an inspection window to see if the shaft is turning? Is it an air vent? What should happen when it is removed? (water drips out, water pours out?..?)

 

[peter anderson]

I've got Grundfos's guide to domestic pumps (11 pages long). It says that the central screw is a vent plug which allows trapped air to escape (which should only be touched when the power is off) and it also provides access to the pump shaft.

 

[GeoffH]

There's my first mistake then. I opened the screw with the system running to check that the pump was rotating. Probably let air into the system. I have also checked the radiator in an unused bedroom and it had some air in it!

Now suspect that I may have air in the system somewhere. Will have to try and get rid of it by opening the bleed valves downstairs whilst having TRVs closed and lockshields open till hot water reaches the rad. This worked last time I re-filled the system.

I have looked at the pump and it is a Grundfos Selectric 4 (4-50/180) which is 4 speed not 3. I have lowered the speed to slowest in case this can slowly move the air. If it doesn't I will try the above bleeding technique when I get a chance.

Ah well, keeps me away from the pub.

 

[gerald]

I dont think its a balancing problem you have if all worked well for a year and now you have the a proble. Just because the pump is rotateing it does not mean it is working correctley. Try this . feel the pipe on the inlet side of the pump to see how hot it is, then feel the pipe work on the delivery side and see if there is a big diffrence in temp. Turn the pupm speed from min to high and listen to the increase in noise level from the pump, there should be a definate change.Final thing what type of control systen is installed is it on a Y plan(3 port motorised valve installed near the pump)?

 

[GeoffH]

Last weekend I tried various things, thinking that there may be an air lock somewhere in the system but had no luck. I am now thinking that it is the pump. Have had a couple of people tell me that they have seem pumps turning, but the impellor has been full of gung and so did not have the "oomph" to push the water around the system. Am going to remove pump and open it up and try and clean it up.

Fingers crossed.

PS I don't have a Y plan. The flow pipe branches off after the pump and goes to separate zone valves (DHW & CH). Both are working fine.

 

[breezer]

if its of any consolation, my pump had a broken impellar.

before you remove pump (and isolate electrical suppy) draw an arrow on the floor /wall as to which way pump is pointing (arrow on pump)

 

[GeoffH]

Good and Bad news

Removed the 4 Allen screws and (eventually) opened the pump.

Impellor was full of gung

Cleaned it all off

Put everything back

Pump no longer rotates
(The operation was successful, unfortunately the patient died!)

Power is getting to pump

Going to fit a new pump at the weekend, which should get the system all working again.

 

[GeoffH]

Fitted new pump yesterday - all is fine. All I need now is some cold weather to appreciate my CH system. Phew it's hot here

Thanks again guys.

Geoff

 

[ColinYounger]

Grundfos Selectric 4 (4-50/180)

Fitted new pump yesterday

Folks, I know this thread is old, but I have a Grundfos Selectric 4 (4-50/130) which isn't working anymore. I'd like to replace it, but want to make sure I get the right thing.

I've tried using the Grundfos website to look for replacements, but it wasn't much help. Know a lot more about sewage pumps now, though.

Any recommendations, please?

 

[ChrisR]

If your pump is 130mm between the ends (where the nuts are) and those nuts are about 52mm across the flats, then a "normal" c h pump will be fine. 5metre head types (eg grundfos 15-50) for up to about 60,000 Btu/hr boiler, 6m for up to 100,000. Those aren't book figures, I just give them as a guide. If your system is marginal then we need more info.

If you have many thermo rad valves then a speed controlled pump like grundfos alpha is a good idea. (as you'll have seen on their web site!)