Cold patches on rad suggestions please =)

[TFGplumbing]

Its a 600x1800 K2 so its a bit of a beast, fed from 10mm drops. I power flushed the system last year as a few of the rads had cold patches; this fixed the problem on the other rads. However this is the largest of all of them and it has a large cold patch In the middle at the bottom of the rad, When I power flushed the system I payed particular attention to this rad but still no joy.

Now I am going back to replace this rad next week and was just thinking could the pipe work be undersized perhaps?

 

[JCplumb]

I think you've answered your own question mate.

 

[tamz]

Yes undersized pipework will be the problem.

 

[DaveTidy]

I'd probably want a bit more info before I'd say it was the pipe size and start upgrading that? You'd think it would be that but if the radiator is red hot on the flow and return, hot over the entire area of the radiator except for a half moon shape in the middle at the bottom then it would still be solid corrosion in the middle of the radiator and a hot flow of water flowing over the top of this.

We used to have a nice thermal image of this proving it years ago.

If you aren't getting a decent temperature across the radiator then I would say it is the pipework size, or the pipework has a flow problem. You can normally see if you have a decent flow by opening a rad valve up into a bucket, the same on the return valve.


I take it once you'd flushed the others you balaned the system again? Try turning all the other off to see if you do get a decent flow and if the rad gets hot all over you will at least know it's a balancing or flow problem and help point toward whether it's pipework size, balancing or corrosion.

Hope this hasn't confused it further but it would be a lot of work to alter the pipework if it didn't need it, best to check first.

 

[TFGplumbing]

I'd probably want a bit more info before I'd say it was the pipe size and start upgrading that? You'd think it would be that but if the radiator is red hot on the flow and return, hot over the entire area of the radiator except for a half moon shape in the middle at the bottom then it would still be solid corrosion in the middle of the radiator and a hot flow of water flowing over the top of this.

We used to have a nice thermal image of this proving it years ago.

If you aren't getting a decent temperature across the radiator then I would say it is the pipework size, or the pipework has a flow problem. You can normally see if you have a decent flow by opening a rad valve up into a bucket, the same on the return valve.


I take it once you'd flushed the others you balaned the system again? Try turning all the other off to see if you do get a decent flow and if the rad gets hot all over you will at least know it's a balancing or flow problem and help point toward whether it's pipework size, balancing or corrosion.

Hope this hasn't confused it further but it would be a lot of work to alter the pipework if it didn't need it, best to check first.

It does get piping hot everywhere apart from the cold patch mentioned, and yes I rebalanced etc etc

 

[REDSAW]

it must of worked ok at time of install so if the pipes are cleaned well...!!!!.

take it off and give it a manual flush and get the mallet out.

 

[stevetheplumber]

unlikley to be under sized pipework if the rad has cold patches undersized would be warm rather than hot

 

[tamz]

it must of worked ok at time of install

Ladbrooks wouldn't give you a bet on that one!

Most rads over about 3kw never heated properly on minibore. The runs were usually too long especially on drops. They het from brand new with a cold patch in the centre in the classic (these days) sludged up pattern and no amount of balancing (even shutting every other rad off) would make it work.

Running 15mm will cure it.

 

[chris watkins]

10mm = 2500 Watts output Maximum @ average rad temp of around 76.5 deg C.
Cold spot in middle (is it on both panels) = debris at the bottom. If you think about it trying to power flush large K2's with only 10mm feeds you are never going to get the water velocities through each panel to pick up & remove system debris 10mm is bad enough through K1's but as it enters a K2 it is either going to go to the front or the rear of course which ever is blocked the water will simple go through the other or over the top on each side.
Before replacing I would as Redsaw suggests take it off & flush with a 1/2" hose first. (standing on end & smacking it with a mallet may help)

 

[diamondgas]

Lets face it microbore's cack!!

Bigg rad. slow flow = debris deposit ...imho

 

[chris watkins]

Just had a quick look at a 600 x 1800mm K2 3.2+kW @ delta T 50deg C so you were all right 10mm is to small, sorry, as ever Tamz was right. (but it does kill me how some thing that power flushing with a big pump but though small pipes & valves is going to work)

 

[jase158]

I had this recently, flushed a system that had 10mm downstairs, went back a week later as still not getting warm, flushed each rad individually and opened up each rad valve to ensure i was getting flow, everything was working.

Replaced pump, still nothing, turned out to be the "H" section (as i call it) the bit where the feed and vent connect into system, just before pump. neutral part of system where sludge was building up

 

[tamz]

Just had a quick look at a 600 x 1800mm K2 3.2+kW @ delta T 50deg C so you were all right 10mm is to small, sorry, as ever Tamz was right. (but it does kill me how some thing that power flushing with a big pump but though small pipes & valves is going to work)

Learned at the school of experience Chris :wink:

 

[chris watkins]

Well we are all doing that, its just that some of us do it at a slow rate !!

 

[REDSAW]

i did say only ok tamz, not great.lol.

power flush is one job, re-piping is another.!.

try it with the customer first and if they agree, then more£££.