Hot Radiators upstairs when heating turned off

[Boatybob]

I have just installed TRV's on all radiators (13) and all radiators heat up with TRVs fully open and overall thermostat (the existing room thermostat in the dining room) at highest level. However, when overall thermostat is at lowest point (10c), and water heating only is selected, upstairs radiators heat up. The pump is external and and does not switch on (I unplugged it and rads still got hot). Is it normal for hot water to circulate the CH system when heating is switched off? My system is non pressurised with tank in the loft, Grant Euroflame 70/90 Boiler, Randall 3060 controller and Grundfos Mark 11 pump.

 

[garrymum]

I don't think you are allowed to put TRV's on ALL rads unless you have some sort of bypass valve or something. Not sure if this is causing your problem though.

 

[powell30]

It's possible your port valve is letting by and you are getting heat transference along the pipe work.....seems if you have disconected the pump the hot water must be getting by somewhere.....i assume this is a Y plan system? (3 port valve to divert from heating to hot water?). If you have disconnected the pump how is your cylinder heating up?......gravity fed? Sorry, give a bit more info and i can be more specific

 

[Boatybob]

Thanks for quick responses. The HW system is gravity fed through one inch pipes controlled by a thermostat on the hot water tank through a Danfoss valve installed in the pipework. The Grundfos pump is on the CH system only and the pipework to the pump leaves the top of the boiler. The return pipe is at the bottom of the boiler. The pump and out pipework are getting very hot (even with the pump unplugged) and the return pipework is quite warm. The rads are warm to hot. The HW pipes leave separately from the other side of the boiler. I cannot see any y valve, would this be inside the boiler.

 

[Soggy_weetabix]

Is it similar to a honeywell 'C' plan system?

You may need to replace the anti gravity valve if you have one

Dave

 

[seco services]

i would say you have a gravity check valve stuck open.

sounds like you have a c plan system with a 2 port valve on the hw return

 

[Boatybob]

Really grateful for all the help you are giving. I am not a pro and will probably have to get smeone in to do the job eventually. However, I do want to understand what is happening and why? How can I tell what type of system I have?

 

[seco services]

the danfoss valve is it a two port and on the hw return from the cylinder ?

 

[Richard C]

Unless you have an anti-gravity or motorised valve on the c/h circuit, hot water will circulate the heating system under gravity even with the pump switched off. I overcame the same problem by fitting a motorised valve on the c/h circuit. This is wired into the pump circuit which is triggered by the c/h room thermostat.

When fitting TRV’s, the boiler must have a by-pass circuit; this can be achieved either with a by-pass loop or, the easiest way, don't fit a TVR to the radiator in the room where the room thermostat is located. Having no by-pass can damage the boiler.

 

[Boatybob]

Yes. The danfoss valve is on the HW system on the return pipe and has two ports.

 

[seco services]

have a look around the pump area for for a brass valve in the pipework about 2 / 3" long.

 

[D_Hailsham]

Does your system look anything like this? If so, you have a C-plan, which is pumped circulation for the CH and gravity circulation for the HW.
(click image to enlarge)

View media item 827

 

[Boatybob]

1. Yes The system is the same as the one shown.
2. Yes There are three valves on th CH pipes. Two ofl them have red taps and appear to be on/off on the out and return to isolate the boiler. The third is next to the pump and has no tap,

 

[seco services]

does the third look just like a brass compression coupling ? sounds like your check valve.
have you any pics ?

 

[Boatybob]

I have put a pic in the album below. Cant work out how to show it in this message. Hope it works.
//www.diynot.com/network/Boatybob/albums/