Column radiators taking ages to heat up and still only warm at the bottom. Help

[mrpaddyseymour]

I have two large column radiators in my kitchen diner. For the last couple of winters they have taken an age to heat up properly and the boiler has to be turned to max to get them to get to this stage. They are big units, 4 coulumns and I understand they take a lot of water.

I have bled them, taken them off and washed with a hose, left chemical in overnight, hit with a mallet and drained the system down. I have also turned off all the other radiators and left them on with no increased performance.

Any suggestiions ?

 

[fuzzy]

are other rads hot?

 

[mrpaddyseymour]

piping hot cause I have the boiler set to max. its a new combi boiler btw.

 

[fuzzy]

have you balanced the system? what type of valves does it have?

 

[mrpaddyseymour]

Not balanced. Just turned off all the other radiators and left those two on. All my radiators are fitteed with thermostatic valves. These two have "old school" tap types. In fact, the flow pipe/thermo is piping hot and the return is only luke warm. Having said that when the rads were of last week being soaked in chemicals, I checked the water and it was coming out of the valves as I would expect. When the plumber changed my boiler he also checked this and said this wasn't the problem.

 

[Best]

Some of those column rads have a diverter in one side, so there is a flow & a return side. Check this, just in case. Those big rads can be quite restrictive, but not all of them, so they are better fed from main pipes & not from 15 mm pipes that are doing other rad or 2. The circulating pump needs to be suitable, but think a combi would have decent pump.

 

[mrpaddyseymour]

The thing is they used to work fine as far as I can remember. When they were fitted they said it was IMPORTANT they were set up for the flow and return in a certain way and made sure I did this. When the rads were off the flow from both the flow and return seemed ok, and this was confirmed by a plumber. Also plumber confirmed the pump should be adequate. What do you mean by restrictive ? Have you heard of this type of thing before ?

 

[Best]

The flow side on bottom of some of those rads has a diverter plate, I think. By " restrictive" I mean a lot of those rads that have very thin or small waterways. Yours may not be those. The water flow may seem ok from open pipes, but that won't prove the pipe is not restricted ( if, say a pipe was very long &/or connected to small pipe, flow could seem ok, but pump would struggle. I have seen circulating pumps that seem perfect & sometimes fairly new, not working well, particularly on the harder parts of system. Also inside of pump can be blocked or impeller even.

 

[fuzzy]

they always work better when the flow is at the top

 

[mrpaddyseymour]

Not sure if there is a diverter plate. They are modern reproduction rads from Wickes and I don't have the impression they would produce them with small waterways. Not sure how the pipes are connected, they are under a wooden floor that can not be taken up. Sounds like I might have to live with this. For the record I have a Vaillant Eco tec, fitted last May. Like I say the rads used to work fine and pipework has not been alterted.

 

[mrpaddyseymour]

I have no choice, due to design, to have the flow at the bottom.

 

[peteplumber1968]

Check the pump sounds like it could be running slow or you have a blockage in the system. You could also shut all rads off and see if you could blow any crap out of the system. I know its a pain when a rad doesnot get hot. Pete

 

[mrpaddyseymour]

Thanks Pete. Already done as you suggest. No change. How do I check if the pump is running slow ? its a new Vailiant boiler only fitted in May this year.

 

[peteplumber1968]

Hi, The pump in that case should be OK but I would bleed it via the screw at the front and check what setting its on.

I have been thinking a bit more and what I did on one job was isolate boiler and connect a hosepipe ( mains pressure ) to the flow pipe then the return on the heating and turn on with all rads closed except the problem rad. The pressure of the water removed any air or crap which may of got stuck.
In my case the problem rad got hot then I balanced the other rads to suit. There could well be a dip in the heating pipes under the floor which is preventing the water flowing round properly. These problems are a pain and I wish I could help more best of luck Pete