DIY Doctor

Cold Radiators

Postby Jnr_81 » Fri Sep 26, 2008 10:18 pm

I've been in my semi-detached for nearly two years now, and have noticed something strange about my radiators. When I turn the heating on, the radiatiors are hot at the top, and cold at the bottom. I have bled them and I'm no central heating expert, but would have thought if they needed bled they should be hot at the bottom and cold at the top?

Anyway, the last radiator in the loop is in my master bedroom and is normally stone cold all over after switching the heating on. Can anyone pass on any advice, and can anyone point me in the direction of a good guide to central heating systems.

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Simply Build It

Postby screech » Thu Oct 02, 2008 11:22 pm

a few suggestions based on a conventional system but you've not said what type of system is fitted.

bypass open too far.

pump worn or impellar blocked

pipework blocked.

zone/mid position valve not opening enough/restricted

if it's a pressurised system low pressure can make it struggle to circulate.
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Postby Steve the gas » Fri Oct 03, 2008 4:28 am

Hi Jnr,

Sounds like it's sludged up - drain off some water out the system at low level to check. If black it needs draining down/flushing out.

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Postby htg engineer » Fri Oct 03, 2008 8:31 am

You're right, if they needed bleeding then they would be hot at the bottom and cold at the top. When radiators are cold at the bottom it is normally a sign of sludge build up, might be worth removing a radiator or two and check for sludge etc - normally causes by lack of care/maintenance (not flushing when new, not flushing when altering pipeowkr and not adding inhibitor).

If you find there's sludge in the radiators (before spending a fortune on a powerflush) you could remove all radiators and flush with a garden hose, drain all piepwork and refill 2 or 3 times, refit all radiators and add Sentinel x400 sldge remover. Leave in and run system as normal, there's no limit to how long you can leave in system, but for the problems you're describing I'd leave in for a few weeks.

You then drain and flush the system and add inhibitors. It will cost you about £30 but will take abit of time removing, flushing and replacing radiators. Alot cheaper than getting a company to powerflush it though, will save you at least £220.

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Postby screech » Sat Oct 04, 2008 11:31 pm

whilst there isn't a time limit for how long x400 can be in the system there is a limit for how long you can leave it in if you want it to do anything, after about 4 weeks the dirt settles back down again as the x400 has reached the end of its useful life (it suspends magnetic dirt so it can be drained out). x400 isn't a strong cleaner but can have an effect if the system is only slightly sludged so i'd say as previously suggested try it before getting a proper flush done to see if it helps. could try it a few times if it gradually makes a difference.
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