Stumped! Hot hater but no CH

[green81]

Hi,

I have a Worcester Bosch Greenstar 24i system, installed in 2009 with a megaflop indirect cyclinder. The primaries are 28mm, split into a 28mm 2-port for heating and a 22mm 2-port for hot water. The 28mm 2-port for CH was changed and is wired correctly.

The issue is if the hot water is on, the boiler stays on but modulates to a low rate. The 28mm return pipe does get hot. The heating on and the boiler modulates down and turns off. It will only stay on if the hot water 2-port is manually opened. However, after a while this has to close as the TPRV on the cylinder kicks in due to the temperature.

IT has been drained, filled, reverse filled, rads taken off and run water into buckets and toilets via hoses, but still no CH. No draincocks on the heating system apart from 2 under the boiler by the filling loop. Any restriction should have moved when reverse filled.

Any ideas????

 

[jackthom]

Starting with both hot water and heating having been off for a while; when the heating only is called for, does the heating 2 port valve open and does the boiler then fire up?

 

[green81]

It fires up, but only for a few seconds before winding back down.

 

[jackthom]

Does the heating 2 port valve definitely open and have you tried opening it manually just to be sure?

Sorry about all the questions but was the valve replaced to try and fix this same problem?

 

[green81]

Hi. No problem with the questions! The two port had failed and needed to be replaced, so was a like-for-like. It has been tried manually.

 

[Steelmasons]

Hi,

it will only stay on if the hot water 2-port is manually opened. However, after a while this has to close as the TPRV on the cylinder kicks in due to the temperature.

Any ideas????

What do you mean "has to close"?...what you mean is you unlatch the HW valve?
TPRV will discharge @ 90c so obviously valve is not discharging due to temp , unless of course the boiler temp is set to 90c.
Me reckons your full of BS... another troll..

 

[jackthom]

With the heating on does the flow pipework get at all warm beyond the 2 port valve or is there virtually no movement of water through the heating circuits. Assuming the pump is running and the valve is OK there would seem to be a serious blockage.

 

[green81]

Pipe above two port gets hot as does return. Able to take ground floor rads off and get short burst of that hot water but it is not pushing round the system.

 

[jackthom]

Are you saying that with heating only the boiler return gets hot but there's no flow of hot water through the radiators?
If there's poor flow I would expect the return to be cold unless there's an additional external bypass.

 

[Agile]

Hi,

IT has been drained, filled, reverse filled, rads taken off and run water into buckets and toilets via hoses, but still no CH. No draincocks on the heating system apart from 2 under the boiler by the filling loop. Any restriction should have moved when reverse filled.

Any ideas????

That seems to be a massive amount of work and the motor valve has been changed.

Has this all been your own DIY efforts?

Exactly what was wrong with the motor valve?

I don't see that any professional would ever do all that rather than simply diagnosing the problem.

The other question never answered is "did the heating work normally immediately before the valve was changed?".

 

[Agile]

My diagnosis is that the boiler modulates back on either CH or HW and that will be due to a limited flow rate.

I would therefore be looking at the pump and any valves in the system before the motor valves.

Tony