Old central heating, radiators hot but hot water tap is cold.

[hamster88]

Hi i have a very old central heating system which has a cylinder. My problem is that all the radiators (upstairs and downstairs) are hot but the water coming out of the hot water tap is cold.

I dont think there is an electric valve to control the hot water as i cant find one. Usually I turn the valve manually to stop water going to the radiators in summer etc.
Im not exactly sure what boiler it is but its a Thorn with an interruptor thermocouple.

Please could someone help me.

many thanks

 

[brightcrow]

Unfortunately, could be loads of things. You could really do with calling in an experienced Engineer.

One thing off top of my head could be the header tank in loft may not be filling system so the gravity side of system, which it sounds like you may have, could have run dry. Be careful if you are not sure what you are doing though.

 

[SimonJohns]

Could you upload a picture of te pipework around your hot water cylinder?

 

[Halesowen1]

If the tank in the loft had ran dry you would not get any water. It would not be cold.
It seems like a problem with the boiler flow not getting to the cylinder, could this valve you switch (summer/winter valve) be stuck? or not turning?

 

[hamster88]

Hi sorry i cant take a better pic as its in the corner of the house. The pipe on the far left goes to the central heating and has a valve to turn all radiators off. I hope this helps.
thanks

 

[hamster88]

this happened about a year ago and my dad changed the thermocoupling in the boiler and there was hot water afterwards. Last week there was no hot water and i changed the thermocoupling and it solved the problem, and yesterday there was no hot water again and i changed the thermocoupling again but there is still no hot water. The boiler was still alight when we changed the thermocoupling everytime and boiler was firing up.

The valve that controls hot water to the radiators is working as i can shut all the radiators off and on.

 

[Billy Bob Bob]

If the tank in the loft had ran dry you would not get any water. It would not be cold.
It seems like a problem with the boiler flow not getting to the cylinder, could this valve you switch (summer/winter valve) be stuck? or not turning?

brightcrow is referring to the small heating tank(not the dhw tank)and if its a gravity circuit this can cause this fault

 

[Halesowen1]

I dont understand how a dry FE tank could stop water heating up if the rads are on the same circuit. If it has no Valve then the water in the heating is the same that would be in the flow to the coil.
It is pumped as the pictures show, so the water being pumped around the heating should be going to the cylinder too, only thing I can say is the valve is not opening up.

 

[Billy Bob Bob]

normally on a gravity circuit the feed and vent come off the coil on the cylinder if it runs dry hot water is the first to suffer,but the upstairs rads may still work if theres just enough water in them,but i agree the system the op has does look like fully pumped with a microversion fitted to the top of the cylinder so it must have some sort of valve

 

[Halesowen1]

But it says all the radiators are hot and we can see its a pumped system.

 

[hamster88]

Hi the radiators upstairs and downstairs work, I cant find any valve other than the manual one which shuts the water off going to the radiators and the one right next to the pump.

 

[Halesowen1]

Is there an air vent on the pipe from the pump as it goes into the cylinder? try this it might be full of air.

 

[hamster88]

there are 2 pipes sticking up with, which looks like a flat blade cap, i tried undoing em but cant. might just be an end cap not sure to be honest.

 

[Halesowen1]

These are air vents, you may need some grips or pliers to open these to release the air.
If you want to make sure add a pic of them.

 

[hamster88]

Hi thanks for your replies, I suddenly have hot water now, but one of the radiators downstairs is cold at the bottom and warm at the top. I tried bleeding it and it has no air. Does this mean there is a blockage of some kind.

many thanks and happy new year