Gravity Fed - Rads Hot with HW Demand

[Graham81]

Sorry being a bit lazy here but on searching high n low on the forum I cannot seem to find the answer; plus I am used to combi probs.

Friend has a gravity system in which when HW is demand his rads get hot. Now he has been told he can set the valve to manual at the hot water tank, but when he does this the boiler fires up?

Can anyone please explain how this setup works & whether this behavior is normal?

Thanks in advance.

 

[Agile]

It all depends on the type of controls and valves!

Probably a failed motor valve.

Why dabble with a friends heating system?

Tony

 

[Graham81]

It's more for understanding at present as the problem is not beyond control yet.

I think I need to get round there to try & work out for myself how it is all working.

 

[possum_jenkins]

Programmer is probably wired up incorrectly.

Has this always been the case or is it a new problem.

If it is gravity HW and pumped heating you shouldn't really need a motorised valve, unless you want the option of CH without heating the HW cylinder.

When HW is called for the boiler should kick in and the HW will gravitate to the coil.

When CH is called for the boiler will kick in and the pump should run also.

 

[londonboy123]

from what I know if you have gravity h/w and pumped heating ( a c-plan) - usually a solid fuel boiler too, you should have an anti-gravity valve on/before your heating circuit to prevent gravity h/w from getting to any rads/warming them up!!

 

[petit_pablo]

If its a fully pumped system thats gravity fed from header tank in loft then i would imagine that the heating valve is stuck open.

If its gravity HW and pumped CH then there will either be a zone valve or more likely a non-return valve on the CH. This will either be stuck open or the spring has worn and is passing.

 

[ollski]

from what I know if you have gravity h/w and pumped heating ( a c-plan) - usually a solid fuel boiler too, you should have an anti-gravity valve on/before your heating circuit to prevent gravity h/w from getting to any rads/warming them up!!

Think by gravity he means vented.

 

[Graham81]

Thanks for all the replies guys. Can anyone explain why when the valve by the hot water tank is set to manual the boiler immediately fires up???

Thanks

 

[ollski]

Are we talking about a valve with two or 3 pipes connected to it?

 

[Graham81]

I've posted a pic up of the setup. Not sure if it is very clear at all but see what you think.

Thanks

 

[ollski]

Its an s plan system with 2 x 2 port zone valves. Both valves receive a permanent 240v live supply even with the clock and thermostats down so as long as the valve is latched open the boiler and pump will run.

 

[Graham81]

Cool thats great at least I know th setup now. Does this throw any light on how/why the rads may be getting hot when the hot water is on then???

 

[namsag]

Sounds very like your heating motorised valve is passing when it is off and needs replacing