Reverse Circulation? (threads merged)

Pics show everything you can see in the airing cupboard. Boiler is directly below in the kitchen on the ground floor. The pipes to the far left coming out of the floor is the flow in and flow out for the rad in the bathroom on the HW circuit. All the rads connect to the return pipe to the boiler under the floorboards.
HTH
 

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I had reverse flow, I had two motorised valves fitted to stop it. However the plumber who did it for me pointed out that if the TRV's were set right should not get back feed anyway.

However only my main house has programmable TRV heads and the flat under house rarely heated.

However hind sight TRV heads £10 each so material cost would have been same but I wanted the contacts in the motorised valve as well.
 
I have a reverse circulation problem on my sealed s-plan system with the upstairs rads getting warm when the CH is off/HW on. I'm getting no solution from the plumber who installed the full system but I'm sure he well knows what the problem is but hopes that I get fed up and go away....

Carrying out my own investigations of the pipework, I notice that the outlet from the HW cylinder coil and rads all connect to the main boiler return within the ceiling space between the joists, above the boiler but beneath the cylinder. The cylinder coil return is def the last connection before the boiler but not by much.

My question is, is there a minimum distance of return pipe that should separate the connections from cylinder coil and rads to prevent reverse circulation??

Many thanks in advance....
 
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Heating zone valve isn't being bypassed which is something that the plumber keeps telling me to avoid talking about reverse circulation.

Something else I notice is that the upstairs bathroom has a heated towel rail which is fed directly from the boiler and not through either the HW or CH valves. The return pipe from this towel rail connects to the outlet from the cylinder coil. Should this not be connected to the radiator returns and is this likely to be the problem??
 
Pics of pipework in airing cupboard as requested.
The small bore pipes coming out of the floorboards on the far left are the pipes for the towel rail.

IMG_0712.jpg

IMG_0713.jpg
 
Hi Cross thread, you appear to be confident that the towel rail circuit is the cause of the reverse circulation and say its acting as a by-pass. Apologies for my ignorance but what is it by-passing?
 
It would seem that the flow pipe for the towel rail is tee’d off the same feed as hot water, so therefore comin on when hot water is called for.
 
Is that wrong? Where should the supply pipe to the towel rail be connected? The supply pipe to the towel rail connects from the main pipe from the boiler and is located before the valves to the HW and CH.
 
Well it certainly would bring on your towel rail with hot water demand, so yes, in theory it’s wrong. It should be fed from flow to heating.
 
Sorry, I think I'm being a bit dense and don't understand what you're explaining....
I thought the the towel rail IS connected before the HW valve so will not come on with the timer. This supply pipe also goes to the CH valve. Is that not correct?

Sorry to be a bit slow....
 
It does go to the ch valve, but it’s before either valve, so whichever valve is calling fo heat, it will distribute via that feed.
 
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