Rads getting hot when hot water selected?

[Headwaiter]

Hi everyone,
I have a gravity fed microbore central heating system. From what I can see without lifting floorboards there is a flow from the boiler to a Myson Aejec aerator which then feeds into the pump, then to the 3 port motorized valve (there is also a 15mm bypass gate valve inbetween the pump and the 3 port vv which is partially open). When I operate the heating only, all rads become hot and it performs exactly as it should. When I feel the pipe from the 3 port vv to the immersion cyclinder, it remains cold, so all is well and being directed only to the rads.
However, when I let the system go cold again (for testing) and I select ONLY the hot water, the 3 port valvle sends the hot water to the cylinder exactly as it should do and all appears OK. The pipe on the 3 port vv for the rads remains cool so happy. Then, after about 10 minutes, I notice various radiators around the house start to warm up? I can't fathom out why the rads would be warming up when only the HW is selected? At first I thought it was something to do with the 15mm bypass but not sure? I've captured the pipe layout on the attachment. Any ideas please?

 

[Agile]

That is not necessarily how yours is connected.

Usually that problem is caused by the return pipe not being ideally connected and that encourages spurious circulation. That is often in a different direction to the normal flow and return on each rad!

Can be difficult to fix without replumbing all the returns.

Can also be encouraged by partially blocked pipes and a cleaning chemical might help in that respect.

The position of the bypass might also affect it.

You should note its current position and adjust say 1/2 turn either side of the current position.

Tony

 

[45yearsagasman]

1-Has this just happened and has there been any pipework alterations?
2-Close the bypass fully off, but make a note of how many turns. Ensure at least one rad is not controlled by a trv, then run Hw only. See if that has any effect on rads heating. Come back with results.

 

[oilboffin]

Could be the cylinder return is not the last connection like it should be

 

[45yearsagasman]

Could be the cylinder return is not the last connection like it should be

Quite correct oilboffin, thats why I suggested turning it off to test. Taking it out of the circuit leaves the cyl return as last tee.

 

[MJGas]

I think the OPs name suggest he might be on the wind up. And I have a clue wh it is

Plus the fact Agile is just spouting from every thing he learned recently in the CC.

 

[AGAS]

 

[oilboffin]

Sorry 45 I didn't read your post properly,put it down to my age mate.Bob.

 

[PullerGas]

 

[oilboffin]

Alright sir dick guilty as charged.

 

[Steelmasons]

spurious circulation.

Hey Terrywookfit , Agile has stolen the word "spurious" from you...

 

[Agile]

That is a word that I have been using for many years!

Generally in relation to spurious radiation from radio frequency transmitting equipment.

But in the context of heating it is also a normal word to describe circulation outside of the normal mode.

I

 

[jeff the gasman]

Did something fall into the header tank maybe?

 

[Headwaiter]

I think the OPs name suggest he might be on the wind up. And I have a clue wh it is

Plus the fact Agile is just spouting from every thing he learned recently in the CC.

I am certainly not winding anyone up, and my username was selected as many other ones I commonly use are already taken up when I joined this site. I did many years in the military and headwaiter is connected to it, though nothing to do with food/wine! Thanks.

I shall try the serious suggestions above when I get home and let you know how I get on. Since I moved into this house the heating has performed as per the OP, but I have had a complete change of motorized valve and 3 port valve body as well as a system flush, but it is still the same. I suspect pipework?

 

[Agile]

That is the first time I have heard of a Head Waiter who is not connected with food!