Downstairs radiators off when hot water on

[gavcradd]

Hi, I have a central heating system with a stored hot-water tank upstairs - For a while, there's been something dodgy with the downstairs radiators, with them going on and off. I've only just recently worked it out.

Whenever I put the hot water to heat up, the downstairs radiators go off. At all other times, they work fine.

Any ideas?

 

[Armo74]

What about the upstairs ones?

 

[gavcradd]

The upstairs ones stay on when they should - and they're always red hot. The downstairs ones are hot (but not as hot as upstairs) normally, then go off when the hot water goes on.

I've read up on here and it seems it could be the pump, does that sound likely? We had the pump replaced a year or two ago, not sure if this was when all of this started. There is a pressure adjustment on the pump, would it do any damage if I just tried turning this up???

 

[Hugh Jaleak]

I would suspect the downstairs rads have a greater resistance in the pipework, water being lazy will take the easiest route. The upstairs get the lions share of the flow from the boiler anyway, then when hot water calls for heat, the flow is then shared between rads and cylinder. What is available for the rads is not reaching downstairs.

May be solved by a few adjustments. Is there a valve on the lower of the two pipes going into the side of the cylinder?