Rads not heating fully

[PaulMartin]

Hi Folks, I've got a strange fault with radiators not heating fully. Four year old system in three floor house with system boiler and unvented hot water in basement. A lot of the rear panels on the double panel rads on all floors are not heating, almost cold. The fronts are hot though some are cooler at bottom. I have cleaned magni filter ( not very clogged ) Checked mid position valve, pump OK, Danfoss TRVs and lockshields good. Have even removed one of the basement rads that was not heating right and flushed it outdoors with hose, clean as as whistle, no black sludge and system has inhibitor. I have also turned off several rads with no difference to others.
Any thoughts much appreciated.

 

[oz-plumber]

Hi Paul,

You may have a pump problem.
The impeller may have broken off the shaft, or it could be full of dirt.

I had a situation a couple of years ago where the same thing was happening on a system.

Disconnected the pump and found the problem - impeller was broken off from shaft

 

[Best]

Pump can also lose its power & only work partly.

 

[oz-plumber]

Actually it could also be a faulty capacitor on the pump motor.

When they go they cause the pump to have less power.
If you can undo the screw at the back of the pump, while the pump is running, and put a screwdriver into the spindle and stop it rotating with relative ease, the capacitor is shot.

 

[PaulMartin]

Actually it could also be a faulty capacitor on the pump motor.

When they go they cause the pump to have less power.
If you can undo the screw at the back of the pump, while the pump is running, and put a screwdriver into the spindle and stop it rotating with relative ease, the capacitor is shot.

Thanks for thoughts folks...I think the pump is OK as I have put a screwdriver on spindle and can't stop it. Also if the impeller was broken then the rads would not be partially heating on all floors surely. The system is clean and there is a filter so would expect pump to be clean. As I said, when I turn off several rads it makes no difference to remaining rads that are on. Hmmm

 

[PaulMartin]

Actually it could also be a faulty capacitor on the pump motor.

When they go they cause the pump to have less power.
If you can undo the screw at the back of the pump, while the pump is running, and put a screwdriver into the spindle and stop it rotating with relative ease, the capacitor is shot.

I did try the screwdriver on spindle, very strong, unable to stop. If the impeller was broken surely no rads would be heating and when I turned off several rads there was no change to others.
Also not convinced it is dirt in pump as system is clean with magni filter.

 

[PaulMartin]

I did check the pump spindle with screwdriver, very strong and not stopping. If impeller was broken surely no rads would be heating. Also when I turn off several rads it makes no change to the others. Can't really see it being dirt as system is clean with magni filter. I know it looks like a pump fault, what else could it be.

 

[Best]

Pumps can work only partly, even if fairly new & no dirt in them. Don't see this often, but it does happen. The pump will appear to be working perfectly, but don't seem to have the power.
Unless you have a nearly blocked pipe somewhere or nearly off valve.

 

[PhoenixServices]

Are all the rads on all floors not working fully? Or just one floor? Do you have different zone valves for each floor?

 

[steadyon]

Just a thought, and you've probably already tried it, but do the double panel radiators have a bleed point for each panel, and if so, have both been bled for each radiator?

 

[Leo21]

Aa above, rads might need venting. Also double rads can block up on the rear ports.

Other than that, it's circulatin issues. Either your pumps not up to it, or the pump is up to it but can't flow enough through a partial blockage.

Or if your house is zoned, the zones aren't opening fully.

 

[Ermintrude]

The impellers can snap off the pump shaft. Had it on a 3" wilo.

 

[PaulMartin]

Are all the rads on all floors not working fully? Or just one floor? Do you have different zone valves for each floor?

thanks to all...yes all rads affected..1 three port valve..heating temp passing through it quickly when boiler fired.
Single bleed points and tried bleeding them. Think I will remove pump and check though if impeller had snapped then I would expect no rads would be heating..thanks again and will report back next week.

 

[PaulMartin]

Hi all...back with the rads not heating completely, turns out rads have never worked right since system installed four years ago...so it's a three story house with more rads than I can count, I'm thinking the standard boiler pump is too weak ? and is it pos to just uprate system boiler pump( unvented cylinder )or a remote secondary pump after three port valve would be better.
Any thoughts much appreciated..thanks.

 

[jtsplumbing]

Your thinking pump, are you sure that boiler is producing the right amount of heat, has the gas been tested

 

[wildcard]

Have you got another 2 port valve controlling the m/flow? I would have done it on a s plan 2x2 ports,sounds like it has"nt been balanced up right.

 

[jtsplumbing]

Check and see what warranty is on boiler ! if still covered call manufacture out

 

[doitmyself]

A lot of the rear panels on the double panel rads on all floors are not heating, almost cold. The fronts are hot though some are cooler at bottom.

1. Has the system been balanced?

2. Is the boiler supplying enough watts to the rads? (See the boiler manual and Stelrad Catalogue, page 44 -Stelrad Elite)

3. Which boiler do you have (make and exact model no)?

 

[PaulMartin]

There is only one three port valve...System boiler Vokera Mynute 35HE. Have not tried balancing system yet though I did turn off several rads making no difference to others.
Even the rads near boiler in basement not heating fully.

 

[jase158]

Turn off all rads except one nearest to pump and let us know what happens!!

 

[Millsy 82]

1st you need to swap the 3 port valve for 2 x 2 port valves or at least put a 2 port in front of the unvented.

How many radiators are there? If there are loads then look at the pipe sizing, boiler size etc. physically take a couple of radiators out and flush them out. if everything is ok then maybe a low loss header with a larger pump on it?

 

[jonnyswamp]

Take off one of the rads with just the front panel working and temp support it and turn it around,reconnect and refill, see what happens
Are the rads round top type? if so they will have a bleed point for each panel

 

[PaulMartin]

yes there is only 3 port, no safety cut out 2 port. Not sure how that would affect flow to heating.
There are about 19 rads...It's 28mm from boiler through 3 port and 15mm to rads and a 35kw boiler.
I did flush out a basement rad that was not heating fully and it was totaly clean.
The problem has existed since entire system was installed 4 years ago.

 

[stevetheplumber]

pipework is under sized a three port valve is realy only good for 50000 btus max you need to remove that and get a 28mm valve for heating and a 22 for ho****er

 

[AWheating]

Do you time the hot water separate to the heating?
When was the boiler and unvented cylinder last serviced?