Central heating pump position

[Wallingford73]

Hi all,

I have a S plan central heating system, boiler on ground floor, unvented tank in the attic (2nd floor) . The pump is currently in a bedroom on the first floor. If I switch on the heating only, water flows and radiators heat up. If I switch on the hot water only the hot water flows up to the tank. However if I have hot water AND central heating, the heating water will not flow up to the attic but the radiators still heat up.

I see 2 solutions, either add an additional pump so there is one pump for CH and one for HW or (and i;m not 100% sure on this one) I move the single pump to be above the HW tank. (of course I can put hot water on at a different time to heating, but that's not ideal)

Any views on this would be appreciated
Thanks in advance
W

 

[ianmcd]

which boiler, post pics of the valve and pump set up

 

[Wallingford73]

Hi Ian, boiler is a worcester bosh greenstar pipe arrangement is in photo hope it maes sense

 

[ianmcd]

nothing sticking out there in that pic, you shouldnt need a second pump, not a good idea to fit one anyway, what is the pump speed set at ? try in on 3 and see if it helps

 

[dilalio]

If this is a recent problem then pump could be struggling to keep it up!
It's an age thing!

 

[Wallingford73]

Thanks both. It is a recent move of the tank from the bedroom to the attic, you can just see the ring from the old vented tank on the bottom of the pic. So tank used to be same level as pump

I guess this could be an extra demand on the pump so it is not keeping up.

I have tried to up the speed on the pump but no difference

 

[JimCrow]

Where is this pipe going to?, also what is the by-pass valve set at?.

 

[ericmark]

On every radiator there are normally two controls, the TRV and the lock shield valve, the lock shield valve should be set so there is a gradient of heat across the radiator so return water around 15°C cooler than the supply water, I have lost count on how many times I have found the lock shield valves wide open, and the system has relied on the TRV's controlling the flow.

Once the system is warm the TRV's will control it, but as it is warming up, if the lock shield valves are not set, then home tends to warm up room at a time, rather than all together, and it could also result in no flow through the DHW hot coil.

Check settings of lock shield valves, it could be as simple as that.

 

[Wallingford73]

Thank. @JimCrow that pipe is out the the bathroom towel rail.

@ericmark I will check that as it would make sense to increase the resistance in the Ch loop to encourage the flow upwards to the hw coil

 

[Madrab]

Any reason for that last 200mm of return from the HW dropping to 15mm?

If both 2 port valves are opening when both are calling (check the 2 port up to the cylinder is actually opening) and the hot water isn't rising to the cylinder then it's simply down to the available head taking the path of least resistance, which must be around the rads/through the bypass.

I'd head round the rads and turn one off after another and check each time to see when it starts to head up to the cylinder.

 

[Wallingford73]

@JimCrow. Bypass valve set to about 4.5