Rad not getting hot

[lukechrissy]

Hi There, I have recently moved into a large house with 4 floors. I have a combi on the bottom floor. the radiator on the top floor is the last one of the string. This dose not get hot no matter how long i keep the heating on.
I understand that the last radiator of a string may never be as hot as the rest, but is there anything that can be done so that the rad dose heat up?

cheers guys

 

[JohnD]

turn off all the other rads and see if this one then gets hot

what pressure is the boiler guage showing?

 

[lukechrissy]

Gauge shoing between 1.5 - 2 atm
sometime it shows between 2 - 2.5

I have tried this once before as a neighbour asked me to (hes a general builder) the rad dose get slighter warmer, but nothing like a rad should be

 

[bengasman]

If it is a 2-pipe system, all rads should get equally hot, as the rads are parallel.
System probably needs balancing, and possibly cleaning.
Be careful with heating advice from builders, most don't quite know how it works.

 

[lukechrissy]

ok cheers, thanks for the reply.

Any chance you could explain what a 2 pipe system is please guys?

 

[Fluffster]

One pipe feeds the flow into each radiator and a second feeds the return back to the boiler.

So you have 2 pipes going to each rad not just one entering and exiting on to the next rad which is a one pipe system.

What size are your pipes?

Pete

 

[D_Hailsham]

Two possibilities: Wrong pump; system not balanced.

Which boiler do you have - make and model?
Which pump do you have - make and model?
What speed is the pump set to?

 

[JohnD]

I am very puzzled that you say, when you turned off all teh other radiators, this one got a bit warmer but not hot

You did turn off every one of the other rads, didn't you? And check that they all went cold?

Was this one hotter at the top, bottom, sides or equal all over?

 

[fraser116]

If there is a thermostatic valve on the non-heating radiator try taking the head off it and making sure the small pin moves in and out freely.

 

[lukechrissy]

John,
After reading your comment,
I turned all the rads off again and did the same as before. This time i turn the rads off, before setting my heating to off.
This time my results where slightly different than before.
The rad in question got hotter, as got as it should be.
The heat was more to the bottom of the rad, it seams the further i moved my hand towards the top, the colder it was getting.

Also my son has a friend who is a plumber who came to have a look at it for me.

He said: There was air trapped in last radiator which is why the top of the radiator wasnt getting as warm as the others, he also said that this was very unusual as usally the air would get pushed through the system. He also said that my pump wasnt powerfull enough to circulate enough water to the top of my house to completely fill the radiator. And whilst he was here he let some water into the heating system. So im guessing there wasnt enough water to completely fill the system.

Dose this sound right to you guys?

Thanks for all the help guys!

 

[JohnD]

...The heat was more to the bottom of the rad, it seams the further i moved my hand towards the top, the colder it was getting....
....... There was air trapped in last radiator ...

1) bleed that radiator

2) balance the system (see http://www.diydata.com/projects/centralheating/balancing/radiator_balancing.php

3) observe the colour of the water when you bleed it. You may have a sediment problem if the system is old or neglected, obstructing flow. This will show itself by the water being black, or by gas collecting in radiators which need bleeding more than once a year. You can give it a simple chemical clean yourself at the cost of half a day's work and £30 in chemicals, though if you have black sediment I would also recommend a Magnaclean which will cost about £100 plus fitting

I am a householder not a pro.

More background on //www.diynot.com/forums/viewtopic.php?t=175736

 

[bengasman]

...He said: There was air trapped in last radiator which is why the top of the radiator wasnt getting as warm as the others, he also said that this was very unusual as usally the air would get pushed through the system...

If that is so unusual, why do all radiators come with bleeding screws?


He also said that my pump wasnt powerfull enough to circulate enough water to the top of my house to completely fill the radiator. And whilst he was here he let some water into the heating system...[/quote]
Air might be pumped through pipes, but rarely through rads. Your pump could be worn, but unlikely to be too small.

 

[D_Hailsham]

He said: There was air trapped in last radiator which is why the top of the radiator wasnt getting as warm as the others, he also said that this was very unusual as usally the air would get pushed through the system. He also said that my pump wasnt powerfull enough to circulate enough water to the top of my house to completely fill the radiator.

It's not the pump's job to fill the radiator. The pressure of the mains supply will be enough to fill the system. You just have to make sure any air present is let out via the bleed valves and replaced by more water; which is what the plumber did. However the plumber is probably right that the pump is not powerful enough to circulate the water because it will not provide sufficient head (pressure) to overcome the friction of the pipes.

Which boiler do you have - make and model?
Which pump do you have - make and model?
What speed is the pump set to?

You say the rad is hot at the bottom and cold at the top. There is always a temperature difference, but if it is a lot that usually points to air in the rad. Sludge give the opposite result - cold bottom, hot top.