All Radiators Cold At Bottom (Some Are New)

[mckayig]

Hi I have read the previous answers given by Gasman and they were really helpful.
Could someone clarify some things for me.
We have 6 radiators, we have replaced 4 and now have problems. When the 4 old ones were taken off the water coming out was pretty clean. So thought the system was OK. At the moment all radiators are warming up at the top and cool at the bottom. On three of the new rads the pipe that is hottest is actually the one on the opposite side to the thermostatic valve, one of the new ones and the two old ones the pipework on the valve side is the hottest. But even so none are warm throughout. What could be the problem? And how to go about sorting it out?

[razza]

Sounds like they need bleeding.

[mckayig]

Sorry but that has been done.. Not any better

[ChillDoubt]

Sounds like you may need some Fernox.

http://www.fernox.com/problem+solving/how+to+sheets/cleaning+a+central+heating+system

[ELVIS68]

Some of my rads do that mckayig, after a good few whacks it seems to clear any blockages.

One day I'll get round to draining the whole lot which I think it desperately needs

[Dizmo]

I purposely built my own cleaning connector for the same 'problem' you have here. I took a RAD off and emptied it and the water was fairly clean. I then hooked up my homemade attachment and blasted the RAD with water. You mank and junk that came out was horrible. Lumps of sludge and black water. I've never used system cleaner but I've heard it does work sufficiently so CDs advice is, advisable!

[Old_Geezer]

You could have gunk at the bottom that needs flushing out. Since you replaced some they may all need rebalancing as well. Plumber should be able to do that for you.

[The Builder]

Regarding the valves....... some TRVs can be fitted on either the flow or the return. They're bi-directional. It's possible that your valves are not, and they've been fitted at the wrong end.

The fact that the water was clean, possibly suggests that, due to sludge, it's not making its way around the whole system, and maybe "bypassing" some rads.

[mckayig]

We did try fitting a new bi directional on one of the new rads and it made no difference. Still the pipe at the other end hotter than the valve side.

[The Builder]

Yes, even with a bi-directional valve, the other end will be hotter because it's the "flow" side.

Is your pipework minibore/microbore (usually 8mm or 10mm diameter) or the more conventional 15mm.

Smaller bores can bung up more easily.

A good flush through the whole system wouldn't hurt. At least you could rule that out. Re-fill using an inhibitor as well.

Another cause could be the circulating pump. Sometimes, increasing the size/capacity of the rads could necessitate upping the pump speed. It all depends on how the system was laid out in the first place. A poorly designed system, for various reasons, can often require a faster pump speed.

Having said all that, if the system hasn't been extended or increased in capacity, and it was ok before, then there's not much left to try.

Stuck-down pins on the TRV valves is not uncommon too.

[mckayig]

Thanks its microbore, and your suggestions on flushing and checking out the TRV's are what we will try next thanks again.

[geno500]

You could try upping the pump speed most pumps have 3 speeds 1 is for a bungalow with a small system 2 is for houses,3 is hardly ever used so you could give it a try but if you do make sure you go up into the attic where the central heating header tank is,it is the small tank in the loft and check that the system is not over pumping you will know this by water coming out the pipe that sits over the tank,the little tank will not overflow because water is going out of the tank to replace what is being taken out of the system,a bit like having a indoor water feature which nobody can see unless they are in the attic lol,best you get the system cleaned out