No hot water

[cnikon]

I have an oil fired boiler, an indirect water cylinder and only one zone valve. The hot water tank was replaced around five years ago. Until recently boh hot water and central heating worked fine. The hot water has to be also selected for the central heating to work.
I am doubtful that the zone valve is working correctly, it is providing a signal to the control to fire up he boiler, but the heated water only gets as far as the inlet to the coil in the tank. The return pipe remains cool. The system was power flushed yesterday,(although the plumber did not flush the coil independently),still no hot water .
I don't understand how he boiler supplies only hot water with just one zone valve, (I assume it's only open or closed). It has worked like this for years ok.
The diagnosis by the plumber is that the coil is blocked.
When the boiler is switched on there doesn't appear to be any noise or movement at the zone valve?
Any advice on how the boiler can supply hot water only and whether a new motor or head may be needed please.

Thanks

 

[Johntheo5]

Have a look at the valve and see if midposition is written on it, it should also have 3 pipes.

 

[terryplumb]

Pics of the zone valve and pipework around it would be useful. It sounds like the valve is closed to central heating until ch is called for ,and the cylinder loop is permanently open. I assume you can never have central heating only, without domestic hot water being heated at the same time ?

 

[cnikon]

Thanks for replying, you are correct that I cannot have central heating without hot water being on. There is very little of the pipework to be photographed, two 22mm pipes next to each other, one has the valve on it. The plumber has said there will be a T joint (somewhere under the upstairs floor ????) where the the return for the coil meets the 22mm pipe. His suggestion is to cut the coil inlet and return pipes,and then attempt to flush the coil with no guarantee of success.He is adamant the valve is working as it switches the boiler on.

 

[terryplumb]

I assume there is no thermostat on the cylinder ?
Is there a feed and expansion cistern that feeds the central heating system / boiler ?
Is there an air vent on the pipework to cylinder coil ?
I think it's unlikely ,but not impossible, for a 5 year old cylinders coil to be blocked.
If you close all radiators thermostatic rad valves ,what is the result ...worth a try !

 

[Johntheo5]

Which one of these does the valve look like?.

 

[cnikon]

I will try closing all the rads,thanks for advice, think a new cylinder might be cheaper in the long run.The thermostat on the cylinder is wide open, there is a cistern for it in the loft,not sure where the vent pipe comes off, but the plumber did mention it The valve is the top one,2 port

Which one of these does the valve look like?.

It's the top one thanks

 

[Johntheo5]

The first photo above, shows a "tapstat" thats the "red" one with the capillary wire which should be attached to the cylinder, note the setting on the tapstat (required cylinder temperature) and then increase it to the hottest setting, it may make some difference but doubtful as the water is hot up to the cylinder coil inlet?, you could slacken the compression nut at the coil say a 1/2 turn and pull back on the pipe until water/air comes out, if only hot water then looks like coil or return line blocked.

 

[cnikon]

Thanks,which end? The hot feed or return? Assume you're thinking air lock?

 

[Johntheo5]

Yes, the hot end first, then, if accessible, the return. There's also a air vent near that tapstat, can you vent that by removing the black cap or whatever.

 

[cnikon]

Thank you, I can make water leaks just by looking at the pipes,bit of a coward I know. Might try it if I get some bravery!

 

[cnikon]

I have just removed the cover of the motorised valve to see if the motor works, it definitely is not. When the valve is held open manually, or to be accurate, (it doesn't seem to matter) the micro switch is making a connection as the boiler will fire up.
I think that a new motor/head will be needed whatever else happens.
The central heating works fine but no flow through the coil with the valve in it's present state , and the coil return pipe remains cold.
There is a bypass valve on the coil inlet pipe which when opened allows hot water to return to the boiler, so it would seem the pipework is clear other than the coil.
Is there any chance that the motorised valve could be causing this problem?
Thanks

 

[cnikon]

Thought this might help !

 

[Johntheo5]

There certainly could be a problem with the motorized valve actuator, but if the CH/rsds are getting hot water then there should be hot water available to the HW cylinder coil, controlled by the tapstat.
If the motorized valve end switch is permanently made (fault) then the boiler shoulf fire at least intermittently and constantly.
What tells the motorized valve to open? is there a programmer or timer that says CH ON/OFF or something like that, what controls the room temperature?, is there a roomstat (thermostat) somewhere like the hallway. There seems to be another white temperature controller to the right of the tapstat and upside down, can you get a close up photo of that.

 

[cnikon]

There is a controller/programmer that we switch the HW and CH on with. The usual way we control the water temperature is by the boiler thermostat. We have to have both HW and CH on for the CH to work. I think once the hot water has reached the inlet of the tank coil(and can't go further) the boiler does switch off,resuming when the temperature drops again. Thanks again for your time