Hot rads when only hot water on ?

[johnrip21]

i have a potterton netaheat profile 50e boiler and when the hot water is on all the radiators on the house get hot ?
Is there any likely/common fault to cause this ?
many thanks
john

 

[MUFC1999]

What sort of system is it Y Plan, S plan or Gravity HW pumped CH, do you know?

 

[johnrip21]

not sure, have only recentley moved in to the property. the hot water cylinder is upstairs with the boiler dowstairs.
whats the difference between the systems ?

 

[MUFC1999]

not sure, have only recentley moved in to the property. the hot water cylinder is upstairs with the boiler dowstairs.
whats the difference between the systems ?

On the front of the boiler if you pull the bottom forward and down, you will see a little red flat switch to the right of the boiler t/stat it will either be next to pumped or gravity, another way to tell is there are 4 pipes coming off boiler, or do you have a Y shaped valve on the system maybe in the airing cupboard

 

[MUFC1999]

If you have a Y plan or S plan chances are yor valve is passing heat to the radiators when in HW only mode, usually down to sludge stuck in valve not allwing to fully close of CH port, if you have a gravity system it could be something like your anti graviy valve stuck open, although they usually stick closed, and usually its onlt the upstairs rads that heat in this case, i hope this is of help to you, let us know if you need to know out else

 

[twgas]

not sure, have only recentley moved in to the property. the hot water cylinder is upstairs with the boiler dowstairs.
whats the difference between the systems ?

On the front of the boiler if you pull the bottom forward and down, you will see a little red flat switch to the right of the boiler t/stat it will either be next to pumped or gravity, another way to tell is there are 4 pipes coming off boiler, or do you have a Y shaped valve on the system maybe in the airing cupboard

There should be a screw underneath holding this on - no wonder most of them are broken

 

[johnrip21]

it is a fully pumped system.

 

[MUFC1999]

not sure, have only recentley moved in to the property. the hot water cylinder is upstairs with the boiler dowstairs.
whats the difference between the systems ?

On the front of the boiler if you pull the bottom forward and down, you will see a little red flat switch to the right of the boiler t/stat it will either be next to pumped or gravity, another way to tell is there are 4 pipes coming off boiler, or do you have a Y shaped valve on the system maybe in the airing cupboard

There should be a screw underneath holding this on - no wonder most of them are broken

Ha ha oh yes sorry, always forget the dam screw

 

[MUFC1999]

As a guess i would say its either your 3 way valve passing to CH when in HW only mode or If you have an S plan set up then your CH zone valve is passing to HW, you could have reverse circulation if your cylinder isnt lass Tee in b4 the boiler, however this would have always been a problem you would imagine from installation, so i doubt it is that, hope it helps

 

[JohnD]

if you post a photo of the pipes, pump and valve(s) around the boiler and cylinder, we can probably identify the culprit.

You have got a room thermostat, haven't you? Have you got thermostatic radiator valves as well? Is there a thermostat strapped to the hot water cylinder?

Is it all rads warm, or just the upstairs ones, or just the ones nearest the boiler?