Motorised Valve and NRT

[RSVR1000]

Hi all,

I'm currently sorting many issues I've had with my HW/CH heating system.

My setup
System Boiler
300lt indirect unvented cylinder.

I have 2 x 2 port motorised valves(S Plan)

I can feel on the flow side of my CH value is getting hot when my HW comes on.
Question: Is it common for the internals within the brass below the motor to fail?
The head was replaced not long ago.

Question 2: Is it worth also fitting a NRV on the return from the central heating so the return from my cylinder only has a path to the boiler and not into the CH?

Lastly, I don't have a system bypass fitted as I never turn my TRV's off on any of my radiators.

Thanks in advance,
Warren

 

[stem]

If the CH motorised valve inlet is close to a hot pipe (i.e. the pipe to the HW supply) then it will get warm by conduction along the pipe, and that's usual. However, the outlet from the CH valve shouldn't be hot, it might still get warm by conduction through the valve body, but once the pipe gets 500cm or so away from the outlet it should be cool. Unless of course the radiators have been 'on' recently.

It is possible for the valve to not close properly and let some water pass through, and if that is the case, changing the head won't make a difference.

Most systems don't have a non return valve and it shouldn't be necessary. I've only seen one used to prevent reverse flow on a badly designed system suffering from reverse flow. To prevent reverse flow The HW return should be the last one (i.e. the closest pipe to the boiler) on the boiler return pipe. But, if the motorised valve is closed even if reverse flow was a problem hot water still shouldn't be passing through the valve, but the effected radiators would be getting warm, which you've not mentioned.

Another issue maybe the controls, in that the valve is opening when it shouldn't be, but in that case I would be expecting it to open fully and the radiators to heat up as well.

 

[RSVR1000]

Thanks for your comments Stem.

My Boiler/Cylinder are in the garage and I can feel heat in the tails on my rads inside the house, can also hear some pipes knocking (old house) so the heat is definitely coming a long way in. I can also tell it is getting through as the pipe for the CH into the house heats up very fast when HW is turned on to heat. I can also feel my HW isn't getting as hot as it normally would be and I think the loss of heat into the CH pipe work isn't helping.

I know one thing, it is going to be a right pain to replace that brass unit with a new one. I've never drain my CH system before and it's not the best time of year to do it. Looks like back to YouTube. I've seen those easyfit isolators but they are about £125 a pop each.

Thanks again for you suggestions.

 

[oldbutnotdead]

First thing is check your controls to make sure the CH valve isn't being driven open when HW is called for. You'll need a multimeter. On your controller, set heating OFF, set HW ON. Make sure there's demand from the dhw thermostat (turn it up high), check for volts at the CH valve motor.
Just for fun, turn cylinder stat down low (so no demand for hw) and check CH valve motor volts again.
Repeat for all possible system states, record the results.

 

[RSVR1000]

Funny you should say that oldbutnotdead, I had a baxi engineer out for an issue (under boiler insurance) and he said my CH wasn't coming on. He replaced the head on on 2 way but didn't want to wire it all in properly so disconnected the wires from the old head and put a connection box in between. Still wasn't working so he put short between the lives. That night I was thinking it worked fines before so decided to have a look and tidy up the wiring. Funny enough when I removed the panel on the junction box I could see the live feed for the CH 2 way value was not connected (not sure how it came out). I disconnected all the cables he put in and ran the wires straight form the CH 2 way and presto, worked as it should.

I was looking at the new head he fitted last year this afternoon and it doesn't seem to line up very well with the brass body. Doesn't seem to open as wide as it should.

I did take the head of and use a wrench to open/close the value manually and the heat came rushing through when I put the HW on. I'm sure the rubber ball must not be making very good contact. It is about 17 years old from memory.

More investigations tomorrow.

Thanks for your help.