Radiators not heating up newish system

[Gasangel]

Hi everyone,

This is my first post on the forum.

About a year a go I installed a combi boiler in a property, the installation was a conversion from a fully pumped system boiler.
the house sat empty for a month or so before a tenant moved in, the tenant has complained that 3 rads don't heat up, after investigation I have found that the only way to get them to heat up is to turn off the upstairs trv's, I have tried balancing rad by rad but as soon as Most of them are back on the 3 problem rads lose there heat. Now I know your all thinking that the boiler is undersized but I can assure you it's not it's a compact 35kw the house is 3 bed with 11 rads, 4 of which are small singles.

I have tried applying f5 ( sludge remover) which has been in a week with no joy ( it has a filter and was originally flushed). Now 2 of the problem rads are in a room which kind of drops down a foot or so lower than the rest of the downstairs the other is in the opposite room (which has 3 rads) 2 are fine.

I have tried bleeding,balancing etc, incidentally the old system heated up fine, all rads have trv's except the bathroom rad.

My next step is 2 swap the flow and return around and try draining the system.

Any advice is greatly appreciated, I have not come across this before whe the heating is worse after converting.

Thanks everyone.

 

[lewisplumber]

Have you checked how close the connections are to each other under the floor just to make sure that they are not too close to each other and bypassing the rads.

 

[SafeGasInstall]

could it be partly block return pipe !!!

 

[Gasangel]

I will check that, thank guys, I'm not sure about the close connections, put a partially blocked return is a possibility, I'm also wondering if the flow and return are linked together somewhere, I think it's gonna be a needle in a haystack job, but please keep the suggestions coming.

 

[ecowarm]

Try removing the problem rads and connecting a hose to each rad valve (1 at a time) flush to a drain while refilling, dont foget to add more inhibitor

Eco

 

[Gasangel]

Try removing the problem rads and connecting a hose to each rad valve (1 at a time) flush to a drain while refilling, dont foget to add more inhibitor

Eco

That's just it they heat up fine when the others are turned off?