CH not working properly

[bennyd]

Hi all,
I would appreciate any advice you can give. I have a gravity fed system with the following equipment:
Baxi Solo 15 HE Boiler
Potterton EP2000 Controller
Honeywell Sundial Y Plan Diverter Valve
Honeywell L641A1005 Cylinder Stat
Hot water cylinder in airing cupboard upstairs
Cold water tank in attic

We can only have the CH on when the HW is turned on, this isnt much on an issue, but this year, the CH doesnt always come on. The HW will heat up and some radiators will get warm, but not hot and 2 radiators barely get warm. As soon as the hot water is heated to temperature the boiler turns off.
I have tried switching the diverter valve to fully open and made sure it can be in the "middle" position but that doesnt always help (sometimes it does).
If i turn the cylinder stat all the way down i can get CH, but then this doesnt heat the water (or at least not much).
I have managed to get the CH on by fiddling with the diverter and turning the CH on and off a few times on the controller, but there isnt a constant thing that always works.

HW works fine on its own.

Does this sound like the diverter valve is at fault or is there another issue with the system?
If you need any further information please let me know.

Thanks

 

[oldbutnotdead]

Is there a pump for the radiators? If there is, is it functioning?

 

[stem]

From your description, it appears you have a fully pumped system with a 3-Port Motorised valve. When CH only is required it winds fully across and closes off the HW outlet. At the same point it makes a small internal microswitch that keeps the boiler and pump running for the CH. These microswitches are known to become intermittent in their operation.

So here's my theory:

When the HW is required, the hot water cylinder thermostat starts the boiler and pump. If CH is on at the same time the valve will be in the centre position. Because both outlet valves are open the flow is shared between HW and CH, so there isn't the full flow available to the CH and the radiators don't get as hot as they normally would.

When the HW is up to temperature, the cylinder thermostat switches off the boiler and pump, and the valve should wind fully across the CH only position, but because the microswitch doesn't operate the boiler doesn't run.

Fiddling with it may just be enough to get the little switch to operate.

So, I suspect that either the valve isn't moving fully across to the CH only position, or the little switch is dodgy. If you are competent with electrics and can use a multimeter it can be tested.

 

[bennyd]

I have a British Gas Multihead G pump just before the motorised valve. I assume this means i do have a pumped system?
This pump is working, i can feel the vibrations and it gets hot when running.

@stem Your theory sounds quite plausible. I think testing the microswitches is the next step. Which wire do i need to test, is it the white one?
I have basic electrical knowledge and i am comfortable using a multimeter.

I have noticed that my valve cover doesnt have the "dimple" on meaning that it cant be replaced without draining the system so i think this will be a job for a plumber. It would be nice to have the knowledge of the possible cause though and to work out potential costs in advance.

 

[stem]

The wire that triggers the boiler is the orange one.

The white wire should also be live (this is the one that the room thermostat is connected to)

You would have to do it under fault conditions and when only the CH was set to be on. Otherwise the boiler could be running from the HW cylinder thermostat live and fed back to the orange wire via the boiler.

 

[fixitflav]

@stem Your theory sounds quite plausible. I think testing the microswitches is the next step. Which wire do i need to test, is it the white one?
I have basic electrical knowledge and i am comfortable using a multimeter.

If you haven't got it, these wiring diagrams might help

 

[bennyd]

The wire that triggers the boiler is the orange one.

The white wire should also be live (this is the one that the room thermostat is connected to)

You would have to do it under fault conditions and when only the CH was set to be on. Otherwise the boiler could be running from the HW cylinder thermostat live and fed back to the orange wire via the boiler.

I cant access the orange wire (or grey), the valve is close to the cylinder (right up against the jacket) and i cant see that side of it very well. I can see roughly where the terminal is, but not exactly. Its upside down from most installation images i see.
I checked the white wire and that doesnt seem to have any power going through it. This is with the controller set to both HW + CH and the boiler fired up heating the hot water and also the boiler off but HW + CH still on (after hot water had finished heating)

 

[Harry Bloomfield]

I cant access the orange wire (or grey), the valve is close to the cylinder (right up against the jacket) and i cant see that side of it very well. I can see roughly where the terminal is, but not exactly. Its upside down from most installation images i see.

Usually all the cables - valve + pump + stats + boiler etc., will terminate in a wiring centre, you should be able to access all of them in there.

 

[stem]

I cant access the orange wire (or grey), the valve is close to the cylinder (right up against the jacket) and i cant see that side of it very well.

I hope it never needs replacing then, if you can't access the wires.

I checked the white wire and that doesnt seem to have any power going through it

The white wire will only be live when both the CH is 'on' at the programmer, and the room thermostat is calling for heat. If the white wire isn't live then the valve will not move to mid or heating only position, it will stay in the hot water position only.

 

[bennyd]

Usually all the cables - valve + pump + stats + boiler etc., will terminate in a wiring centre, you should be able to access all of them in there.

Thanks, thats correct. I opened that up and got nothing on the orange and white and got 16V on the grey. This was again when the boiler was fired up and down with CH +HW set to "on" on the controller.
If i turn the cylinder stat down to 0, the boiler fires back up and i have heating. I still get nothing on the white and orange and also nothing on grey (which is to be expected as grey is hot water i believe?)

 

[gas112]

motorised valve is knackered if it has a dimple on the cover you can change just the head . The corgi ones from tool station fit and are half the price of honeywells