Radiators Not Heating Properly - Pump Faulty or Not

[Goeser]

With my Potterton Promax Combi HE Plus A, the radiators downstairs don't heat up properly. Upstairs work quite well but when they are turned on the downstairs will not heat up at all. I have removed them and flushed them and also used a cleaner but this hasn't cured the problem.

With all radiators turned off except one downstairs and the locks shield turned up to maximum it still won't heat up properly.

The heating flow and the heating return seem OK and are both very hot to touch. The pump is also hot to touch and vibrates as if it is working OK.

Most of what I have read point to a problem with the pump. I removed the pump head the checked the impeller and it is spinning OK.

Any ideas would be appreciated. Could it still be the pump?

 

[terryplumb]

Has this problem recently surfaced,did the system work fine at some point ?

 

[oldbuffer]

1. Pump could be worn and less efficient than when new, but if its circulating OK for upstairs, less likely to be the problem.
2. How are the downstairs radiators fed, by pipes coming up from the floor, or by pipes dropped down from the ceiling above. If on drops the problem could well be air locking.
3. Are upstairs and downstairs in different zones, i.e. with separate thermostats? If so, could be one of the zone valves.
4. Have you bled the entire system while cold?

 

[Goeser]

terryplumb
I think about 2 weeks ago I was toping up the system and added to much water. Decided to drain some of the excess water from a radiator air vent when I noticed that the water was very discoloured.

So decided to drain the sysem down a few times to clean it out.

Still dirty with sludge so took them off and flushed, still no good so have added cleaner.

 

[Goeser]

oldbuffer
1. Pump could be worn and less efficient than when new, but if its circulating OK for upstairs, less likely to be the problem.

Yes it is circulating upstairs but I was thinking that it would be easier for the hot water to get there than downstairs.

2. How are the downstairs radiators fed, by pipes coming up from the floor, or by pipes dropped down from the ceiling above. If on drops the problem could well be air locking.

As the area where the boiler is situated has a concrete floor, the pipes go up from the boiler into a loft area and come back down again to under the floorboards.

3. Are upstairs and downstairs in different zones, i.e. with separate thermostats? If so, could be one of the zone valves.

The boiler was changed about 6 years ago and although it had been set up with separate heating controls for upstairs and downstairs previously, this set-up was removed when the new boiler was installed.

4. Have you bled the entire system while cold?

As far as bleeding the system goes. Yes, I have been bleeding radiators when cold. Could it be air trapped in the boiler? How can I tell if that's the case?

 

[terryplumb]

But did the system work well up, and downstairs, before you started draining down etc ?

 

[Goeser]

terryplumb
The upstairs part of the house isn't used very much nowadays so heating hasn't been used apart from heating the upstairs bathroom at a reduced setting in frosty weather. So really can't tell how well it was working.

I think what drew my attention to there being a problem was that the thermostat close to the boiler kept switching itself off. So heating would have been working OK apart from the thermostat switching off. How well I'm not sure as weather was not as cold and less radiators were being used. But would say, better than now.

 

[Goeser]

Other things I have done to try and improve the heating has been to change the valve assembly in the diverter valve because of a small leak and replaced Automatic Air Vent.

 

[terryplumb]

Turn down fully off ,all the lockshield valves on upstairs radiators ,(leave their TRVs open). Open all downstairs rads lockshields fully and also their TRV s. Run heating and see if downstairs rads heat fully.

 

[Goeser]

terryplumb
Done as you requested and here are the results.

Upstairs: All radiators cold.

Downstairs: There are 2 small radiators at the back of the house next to the boiler which are really nice and hot. The other 4 larger radiators are cold including the living room which I was getting at least some heat before because I had turned the others off to enable heat here.

So, looks like only a certain amount of heat is being produced and looks like those closer to the boiler are getting it.

Also, is it possible that these smaller ones are on a different system because when I drain the system down, these 2 seem to hold water in them.

 

[terryplumb]

Close the Trvs on both hot rads ,see if other downstairs rads heat up.
( Leave all others as before) I suspect your pump is the problem.

 

[Goeser]

terryplumb
Closed the Trvs on the hot rads and now the other rads have only a faint heat. Reverted back to original. Which was, all rads off except the one in our livingroom which although it doesn't get hot enough, at least gives off some heat.

 

[terryplumb]

From what you have told us ,the pipework goes from boiler on ground floor ,up past the rads on first floor ,into the loft and then back down to ground floor rads. That is quite a long circuit ,no idea what pipe diameters are involved in that run ,and no confirmation that the system ever worked fully since the changes to the system and boiler.
So it appears to me that the pump is inadequately circulating ,the system is not balanced ,the thermostat may be an issue ,and the system would benefit from being cleansed. There is no substitute for an on site investigation by an engineer ,which you should seriously consider. Regards Terry.

 

[Goeser]

Terry,
The boiler is located at the back of a ground floor kitchen extension where the 2 small rads that previously heat up to full heat are situated.

The pipes from the boiler which are 22mm go up into the loft area above and must come back down to these 2 small rads which use 10mm pipework.

The main 22mm pipes run on about another 10 feet in the loft space before dropping down to go underneath the floorboards to feed the other 4 larger rads on the ground floor.

In the loft space these 22mm pipes continue to run at this level to feed the upstairs rads.

Yes the system has worked fine in the past since the system and boiler change.

Which thermostat do you think may be faulty?

Cleaner in system at the moment.

I think it would be worth while trying a replacement pump head which would eliminate that at least. If that worked, balancing the system should be easy enough.

 

[terryplumb]

Are the rest of the downstairs rads tubed in 10 mm ?
The thermostat that you mentioned in an earlier post ,may not be in a good location ( not necessarily faulty) and cutting off the boiler prematurely ,think you said it was near the boiler ??