Central Heating Issue

[hiretools]

Hi Guy's Just wondered why radiators heat up when the boiler is switched on but each time it is one rad stay's cold it's an old back boiler system which has just had two new single rads installed. Yesterday the bathroom one never came on the day before it was the back bedroom and today it was the downstairs hallway any ideas would be gratefully received. Cheers Tony.

 

[PlumbBobBob]

sounds like there could be air in the system being chased round the system. have all the rads been bled and any other air vents

 

[diamondgas]

Thermostatic rad valves fitted maybe?

 

[hiretools]

Sorry for appearing dumb. But what has thermostatic valves got to do with the above stated problem. Yes the new rads have thermo valves and all the older rads don't. But why do some of the old rads stay cold and not just the new ones. ?? pls Help!!!!

 

[diamondgas]

TRV's switch off on room temp which could account for individual radiators turning on and off 'randomly' However you state you haven't got them on the older radiators so it won't be an issue!

As steveb has said it could be down to air? If not then it may be that your system balance has been knocked out of whack, restricted flow in the system....? Most likely air as it's alternating radiators rather than a specific one or two!

 

[hiretools]

Thanks m8 I will belled all the rads and see if it rectifies the problem. Do you have a certain way of bleeding the rads ie: bottom rads first or vice versa thanks again Diamond

 

[diamondgas]

Thanks m8 I will belled all the rads and see if it rectifies the problem. Do you have a certain way of bleeding the rads ie: bottom rads first or vice versa thanks again Diamond

It doesn't matter, all you're doing is filling them with water. Best done with the system turned off though! If it is air you could try turning off all but the troublesome one/s let the air be pushed into the radiator where it can't escape. What size pipes supply the radiators do you know, 15mm,10 0r 8mm?

 

[hiretools]

all the rad pipes are 15mm D..

 

[diamondgas]

15mm pipe rarely gives serious circulation issues, it may indicate a blockage/restriction somewhere or a failing pump? Not an easy one to diagnose without first hand tests and checks to be honest. I hope its air

 

[hiretools]

So do I m8 these old back boiler jobs are a naus ache I will shut down the rads apart from one and bleed the system and see what happens thanks for your help m8 I appreciate it. Cheers Tony.

 

[diamondgas]

Your welcome Tony Let us know how you get on! 15mm pipe should heat up quite quickly. If one of the pipes is mad hot and the other a lot less hot is a good indication of poor circulation. On an old system you're expecting around 11 degC difference between the two and an even surface heat across the rad Good luck!

 

[mountainman]

Isolate and drain the furthest rad, loosen and turn a valve so it discharges into a bucket.
Turn on valve fully for a few seconds, any air in pipe should be pushed out.

Repeat process on other rad feed, reconnect and vent rad.