Hi all, I'm getting frustrated and hoping someone can help. I have a heat only boiler with a hot water tank. The house has an extension and the 3 rads in the extension wont get heat. Two of these rads are brand new. They were in 10mm pipe before but all are now in 15mm. We also got rid of the tank in the loft for the central heating and replaced with a Robokit hoping that moving to a pressurised system would help. If I turn off most of the upstairs rads and some of the better performing downstairs ones then I start to get some heat into the new ones. They are obviously furtherst away and the system just can't manage it all. My plumber is now suggesting a new boiler as it does appear that my 24kw heat only is a little undersized for the house (14 rads and a hot water cylinder) I've tried balancing and it helps a little but still can't seem to get these end rads hot unless I just totally shut down other rads. Does this sound like something that could be fixed with say a 30kw boiler or should I be looking at other things? Thanks in advance
The rads upstairs are barely open at all. I can try further balancing I guess. Could an undersized boiler not cause this issue then?
Unlikely ,but the pump may be suspect if balancing doesn't solve the issue. Close every other rads lockshield valve ,once the 3 heat fully ,go around the others ( one at a time) crack open the lockshield a little till that rad heats,then move onto the next rad.
Some of the rads have had TRVs fitted on return side, can I still balance these on the flow side for now? Plan to sort that out in future
Yes,whatever side the lockshield is on use it. Are any of the rads that don't heat fully vertical " designer" type rads ?
Do you have a Y plan system ? You don't want the programmer running hot water when you are balancing rads ( i.e. not heating the hot water cylinder)
Maybe obvious, but Have you tried the heating with the hot water definitely off? When the 10mm was replaced, was ALL of the 10mm removed?
This one can handle it either way. I've just turned the heating on with all but two of the new ones on. I can't get to the 3rd one today as my new kitchen is stacked in front of it. The flow pipes on the two are piping but the rads are taking their time to heat.
There's no 10mm involved at all with these problem rads. Some of others have some 10mm but are working fine.
Do you mean every other rad is turned off ? If so and your two problem rads are not heating fully ,quickly , then there is a plumbing issue, possibly on the return,or their valves.
One unpleasant possibility is that when the extension was built, the radiator feeds were simply piggy backed off another radiator. Even in 15 mm there is a limit to the amount of heat the pipework can pass, generally reckoned to be around 4 or 5 kW. If the radiator used as a source, plus the three new radiators have a total heat capacity greater than that, they won't heat properly. If this is the case you will need to look at connecting the three to the main heating "spine" - usually 22 mm pipe.
This was actually the case but we fixed it. None of them are piggy backed now, they are all piped individually in 15