DIY Doctor

Main navigation

Cold Downstairs radiators

Postby darren popham » Mon Jan 05, 2009 2:04 pm

I have checked Projects and other posts but would like some guidance!
I have a 10-15 year old house with double glazing so should be reasonably insulated with a conventional gas boiler and radiators. Upstairs is fine (bordering on hot!) but downstairs is cold. Radiators get warm but never "to hot to touch unlike upstairs. In fact when its cold the downstairs never gets warm enough to turn of the rom sta (it clicks at about 18). I have had system power flushed last year, i have balanced system (upstairs all have return valve almost closed) upstairs is better but downstairs still cold. I am concerned could be boiler or pump and plumbers dont seem to want to help diagnose only do jobs you tell them so a couple of questions:
1. The boiler sems to come on and go off quite regularly, if stat not turning boiler off should it not just stay on? Is this oeprating correct.
2. We have 13 rads and I wonder if pump not working but if I check the pump it is spinning. Would a better/newer pump help?

Any thoughts much apprecaited.
darren popham
Rank: Apprentice
Progress to next rank:
Posts: 6
Joined: Mon Jan 05, 2009 1:56 pm


Simply Build It

Postby htg engineer » Mon Jan 05, 2009 7:20 pm

Are the upstairs and downstairs radiators connected with the same size pipe. All 10mm or all 15mm.

Have had problems where all upstairs were piped in 15mm and all downstairs in 10mm, obviously there's more restriction in the 10mm and the upstairs radiators were starving the downstairs.

Also worth checking the pump, put on max speed III, check condition - might be worth renewing.

htg engineer
Rank: Project Manager
Posts: 3256
Joined: Tue May 22, 2007 5:22 pm

Postby darren popham » Tue Jan 06, 2009 9:28 am

Very kind of you to reply.
Unfortunately the house is on micro bore pipes, other than two new rads fitted upstairs after extension. Which are on "normal pipes"

I have the pump always on top speed, ( I have bled the pump and also checked its spinning freely which it is).

The boiler is always on its top setting but seems to come on/off quite intermittently even if the room stat and hot water tank stat are on. I have a thermometer which measurers the water output at about 49degrees. is this right???

The rads downstairs do get warmer at top compared to bottom, and I have checked
darren popham
Rank: Apprentice
Progress to next rank:
Posts: 6
Joined: Mon Jan 05, 2009 1:56 pm

Postby Steve the gas » Wed Jan 07, 2009 6:00 am

I would be suspecting sludge/blockage - rads cold at bottom.

If your skills are up to it , I would drain and refill a few times then after proving it works add inhibitor.

Dam microbore pipes.

Steve the gas
Rank: Site Agent
Progress to next rank:
Posts: 780
Joined: Sun May 04, 2008 7:07 am

Postby darren popham » Mon Jan 12, 2009 11:34 am

Well, found out now that my boiler Ideal Classic NF40 is only providing water at 50degrees even on the higest temperature setting. (I know this as I bought a thermometer to check!!) Spoke to Ideal but they are know help just say "get someone in". Can any of you plumbers or heating engineers give a suggestion as to whats likely to make the water only heat to 50degrees, I guess a thermostat or similar but then Im know plumber!!
darren popham
Rank: Apprentice
Progress to next rank:
Posts: 6
Joined: Mon Jan 05, 2009 1:56 pm

Postby Cav » Sat Jan 17, 2009 3:47 pm

Darren, have you tried closing the rad valves (both ends) on the rads that get warm to see if the hot water can get elsewhere round the system?

Microbore pipes are a pain, and nearly impossible to unblock if it's really bad

DHW should be set to 50°C out of the taps
Rank: Labourer
Progress to next rank:
Posts: 3
Joined: Sat Jan 17, 2009 3:05 pm

Postby corgi bod » Sat Jan 17, 2009 6:14 pm

Hi Darren, sounds like either boiler stat is faulty or gas burner pressure is low. Unlikely to be sludge if you have already had it flushed. Sometimes pumps can still run but not turn the impeller. Burner injector may also be partially blocked. A service will show up any boiler faults. Don't try adjusting gas pressures yourself. Hope this helps.
corgi bod
Rank: Labourer
Progress to next rank:
Posts: 1
Joined: Sat Jan 17, 2009 6:04 pm

Postby TheDoctor5 » Fri Jan 23, 2009 9:30 am

Last year 64% of the questions asked in our forum were answered within our DIY project pages at The project pages are now separated alphabetically and your answers are accompanied by diagrams and the ability to see, and buy, the tools and/or required to complete your project. Use our search box to look for your answer and save a great deal of time and money!
Posts: 1381
Joined: Tue Jan 20, 2009 9:17 am

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics