Central heating radiator mystery...can you help?

mikeluxy

I am trying to sort out an ongoing problem with my Central heating...basically down to cold radiators and some only getting luke warm.

I have a Viessman Vitodens 100w installed in 2009.

For an experiment I turned off all radiators in the house and opened up the valves on one radiator at a time.

On each occasion each radiator gets stinking hot...indeed every radiator I tried (upstairs and down) heats up fine however if I try to turn on another radiator at the same time it wont heat up and remains cold.:mad:

It seems the boiler will only seem to heat one radiator at a time....

Surely there cant be a blockage as each individual radiator heats up if selected individually.

Could it be down to a faulty boiler...?

Any ideas as to this puzzling mystery...?

SailorSam

I think you may need to balance the system.

Balancing And Setting Up Central Heating

mikeluxy

The mystery is that one radiator on will get so hot that you cant keep your hand on it (as it should be) but if more that one radiator is selected it goes down to "warm" and gets progressively cooler the more rads are turned on...we have 9 rads in total....im leaning towards a boiler fault as it cant supply enough heat output to all the radiators...?

Flapawack

Do you have thermostatic radiator valves fitted? TRV's

mikeluxy

On some rads not all

Flapawack

This is a strange one . . Has your system ever worked properly? And is there a bypass valve fitted?

gas4you

Could be a pipe sizing problem.

What size pipes/type of system do you have?

bengasman

If the system was fine last year, and you didn't change anything until now, there is probably a fault.
Could be anything from faulty pump, faulty sensors, pcb, gasvalve or sludged up system.

1. Do NOT do anything yourself, as this can void your warranty.
2. Check that the boiler benchmark is filled out correctly and signed off complete with installer registration number.
3. Contact the installer.

mikeluxy

Thanks everyone for your on going help on this...much appreciated.

Just one observation though...The system was flushed out before the new boiler was fitted and (as mentioned) if I select one rad at a time then that radiator will heat up practically straight away with no cold spots and no problems....this would suggest that its not a sludge problem...?