One radiator hot when heating off - Plumbing Forum | Plumbers Forums

user123 · 10-09-2008

Please can you advise on the following.

One radiator is getting hot when the heating is off, but the hot water on. (modern sealed system, baxi condensing boiler, ariston cylinder, two pressurisation tanks, all thermostatic radiators). I am pretty sure it didnt used to do this.

This radiator is on the top floor of a 3-storey house, directly above the airing cupboard.

None of the other radiators are getting hot (although this morning have noticed that the feed pipe to a couple on the middle floor are warm).

Having looked at the pipework in the airing cupboard it looks as though this radiator is plumbed to the by-pass loop, so I assumed maybe that hot water was being bypassed when it was getting too hot. However this morning when monitoring the situation the pipe feeding this radiator seemed to get hot immediately, so am not sure now about that theory.

If a valve was faulty would all the radiators, at least on the top floor, get hot. The one that gets hot is very hot (the other one up there is stone cold).

My theory about the by-pass aspect was also linked to the fact I thought the hot water seemed to be hotter than usual over the past few weeks (maybe being paranoid).

Also a few weeks ago we heard a metalic type tinkling noise in the pipework in the airing cupboard which seemed to happen when using the hot tap, and then the cylinder filling with cold. This only occured for a couple of days and then stopped. Possibly completely unrelated.....??

I am trying to work out what is wrong before jumping the gun calling anyone out........

user123 · 10-09-2008

Hi Thanks

Yes two of the honywell type valves.

The arrow on the picture shows the pipe that leads to the radiator that was getting very hot. I tried putting the heating on tonight (no water) and the pipe only got warm, whereas the larger diameter pipe, below the T joint was very hot.

If it was passing could one radiator get very hot and none of the others be affected?

Cheers

user123 · 11-09-2008

Hi Thanks

Fired up this morning.

Both sides of HW valve hot (front of pic).

Pump side of CH valve hot, other side cold after 10 mins or so.

Radiator pipe with black arrow very hot very quickly (to upstairs rad). 15mm radiator pipe near to cyliner (left hand of pic) (from upstairs rads) warmish after 15 mins or so, which then made the connecting pipe (i.e. radiator side of CH valve) warmish.

This is why i had originally thought it was part of the overheat bypass......

user123 · 11-09-2008

Thanks for the reply, sorry about all the questions.

I think it has only just started doing it, but it is a thermostatic rad up there and with the room being in what would be the loft it can be warm up there anyway, and may have turned itself off in the past...just a stab in the dark...

I think the pump does overun after the valves have shut.

Thanks again for the replies..

fuzzy · 20-09-2008

im pretty sure you are getting reverse circulation, its using the arrowed pepe as a flow and not a return and finding a route back, the bypasss should be the last tee on the system(return ) and before each 2 port valve, its possible that this is only hapening when the pupm over run is on as both motorised valves will shut.

i would put in a auto bypass valve and adjust the piping on the by pass