Rads go cold when hot water is on

[darreny]

hopefully someone can help me out here...

I've just had a new boiler installed along with a megaflo and 3 new radiators in our newly built extension.

After it was installed the central heating worked fine, but when just the hot water was on the new radiators also heated up (hot...not just warm.) The plumber has come back and I think has installed a non-return valve on the 'return' of the megaflo.

Now...the radiators no longer heat up when the hot water is on - good news. The central heating works fine and all radiators are hot...until the hot water also turns on - then the three radiators go cold! All the other radiators are fine and stay hot.

I'm confused - so is the plumber! Any ideas would be most welcome.

Thanks,
Darren

 

[tamz]

He has obviously piped it up wrong and no one will be able to tell you without seeing it or a drawing of how he has done it.
For a start he has teed the return from the new radiators into the wrong position.

 

[smillsey]

Did he definately have Unvented G3?

How the hell people install these wrong I dont know. We all make mistakes I suppose, but read the MI'S!

 

[tamz]

Having a G3 don't mean you know how to install heating😛

 

[smillsey]

ha true tamz,

however having a G3 means he paid 200 quids to sit down all day and earn no money

 

[tamz]

Also true smillsey. And also proves he can read and stay awake🙂

 

[Gray0689]

Also true smillsey. And also proves he can read and stay awake🙂

Not really tamz a monkey could pass unvented sleeping lol

 

[tamz]

Shhhhh😀

 

[justlead1]

Is it as simple as the motorised valve is wired to give hot water priority? (when it occurs turn the cylinder stat down to nowt and feel if the rads come on) Good Luck

 

[darreny]

Justlead1 - I tried your suggestion. When I turn the megaflo stat down to 1, the radiators do get warm but not as the other rads in the house. If I turn the hw off they heat up properly. Also, if the HW and CH are on together and I turn the megaflo stat back up then the three rads go off....

 

[smillsey]

darreny we would love to help but you need to get the guy back round. Without seeing whats going on in the flesh its very easy to chase your own bum when posting on forums especially with unvented....

Sorry I cant be of any help

If you have no luck with him perhaps post up in the "i need a plumber" section,

it will cost you but the chaps on here will be the best out there 😉

Seriously, the most serious plumbers/Heating Engineers are always "Geeking" it up on forums.

 

[stevetheplumber]

this being unvented is realy irelevent to the problem sound to me that the tees for the hot water circuit are in the wrong place they have to be the tees nearest the boiler

 

[justlead1]

Hi, I sounds like the guy that has added the three rads, has stabbed a F&R to the rads from the easiest place and not the best place. I would be inclined to ask him to check out the problem and come up with a solution. It also can be that the actual room temp has been reached and the rads cool via thermostatic valves, it all worth checking out.

 

[Gray0689]

Sounds like when heating coil just running round it (taking path of least resistance)
Get jim to but a gate valve on coil to throttle it down

 

[Plucky]

Sounds like when heating coil just running round it (taking path of least resistance)
Get jim to but a gate valve on coil to throttle it down

As above,

has anyone actually read the OP. If the tee was in the wrong place then the symptoms would be rads getting hot when HW only is selected.

If rads are colling when a demand for HW is in place then the system needs balancing. This is achievable by placing a gate valve on cylinder return and throttling down bit by bit.