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old radiator valve replacment

Postby uk_ducati » Tue Jun 24, 2008 5:56 pm


i am about to change my radiators and valves for new ones. at the moment i have 8mm micro bore and 2 pipes enter into 1 valve. the other side is just blanked off. is it ok to take 1 pipe to the other side of the rad and fit a lockshild while fitting a trv on the other side. ( i am assuming that the 2 pipes into the 1 valve are still flow and return.)

also the bar pressure at the boiler for the radiators is at 3.4 bar and climbs very slowly through the year. to reduce the pressure i have to bleed a rad. what could this problem be.


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Postby plumbbob » Wed Jun 25, 2008 10:53 pm

The installation you describe with the flow and return via one valve is no longer legal, so if you are replacing radiators, you must replace both valves and connect in the conventional way. Don't forget under new legislation all but one of the valves must be replaced with thermostatic models.

As for the system pressure increasing, it may be an internal fault with the boiler (oh dear) but the first thing to check is the filling loop. If the valve fails to shut properly, the system will overfill over a period of time. It is not a good idea to allow the system up to this pressure as it may cause the pressure relief valve to operate or some other failure.
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Postby htg engineer » Thu Jun 26, 2008 2:59 pm

Yes the valve has the flow and return connected to it, there'll be 18mm pipe inside the radiator too going to the end with the blank on - this ensures the water circulates.

Pretty simple to change as you have to flow and return there, it's just a case of extending one pipe to the other end, you can normally get one of the pipes to fit the new radiator without extending it - just a new rad valve.

All the regs state, is that TRV's have to fitted to at least all sleeping areas. They recommend you fit them throughout the dwelling, but is not a legal requirement.
As for the pressure rising, disconnect and cap off combi fill, if it's still rising, it could be a problem with expansion vessel or plate heat-ex. Rising 2.0 bar over a year - not a problem.

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