New Vaillant 418 with unvented problems

[SPC]

We recently fitted a new vaillant 418 and range tribune 180l unvented cylinder at a friends house with powerflush, magnaclean etc etc but he is having problems with his hot water.
Old cylinder position was the airing cupboard on the landing new position next to the new boiler in the garage. Problem he is getting is on all of his hot taps the water is going cold then hot even though there is a full tank of hot water. It happens whether heated by the immersion or the boiler. Anyone had any similar experience? Can't ring kingspan/range until Tuesday now!

 

[Chalked]

Sound like cold is being mixed back. Probably a shower mixer with no check valves

 

[ShaunCorbs]

turn the cold off to the cylinder and start opening hot appliance / outlets any running?

 

[Gasmk1]

Now the pressure is greater for the hot water it will be as said above a shower or mixer tap check showers first as they might have been low pressure

 

[townfanjon]

Yep vented to unvented usual problem.

SPC please report back mate

 

[SPC]

An on suite shower has the original shower still in it was fed from a shower pump before no check valves unless the old pump had any in, however that cubicle is leaking badly so it's not in use. The main bathroom has a bath shower mixer on the bath, the type with the bath connectors which takes the 180 centres down to 150 centres so you can fit any wall mounted bath shower mixer to it so the old one got replaced with a new hansgrohe bath shower mixer (didn't have to take the bath panel of but I'd guess no check valves). I recall the cold main pressure being particularly high though.

So it seems my first options are:

A) Install a pressure reducing valve on the incoming main to make sure it's no more than 3 bar therefore theoretically somewhere near equal to what will be in the cylinder.

B) Install check valves at any mixing appliance

C) Both

Also question, could I be using the main bathroom bath shower mixer and the water be mixing through another appliance like the old en suite shower valve to create the hot/cold fluctuation at the main bathroom.

 

[SPC]

turn the cold off to the cylinder and start opening hot appliance / outlets any running?

I'm going back either tomorrow or Tuesday so I shall double check this then. There is an old basin downstairs with separate hot and cold taps perfect for checking that. Good idea

 

[Chalked]

If the cylinder is piped up correctly, non returns are not needed.
Take a balanced cold from the combination valve.this will cure it.
On a side note, just because the other mixer is off. This doesn't mean it won't mix. Some mixers have the thermostat before the on/off, so can pass cold water o hot, even when off.

 

[SPC]

To retro fit the cold main directly to the tank and utilise the balanced cold would be very awkward, but not impossible. I'll go take a look at it all and see whats happening and report back

 

[kris]

Right your saying it runs cold then hot , how long for and does it fluctuate back n forth or does it run cold for long ?? he does realise that he has a bigger dogs leg now lol , with tank now in the garage ,
As previously said id be looking at mixer tap or shower ,
( or an apprentice when removing the CWSC didnt connect the cold main to the vent pipe ) lol kidding ,

 

[SPC]

Lol Kris, my apprentice has become the master. . . Joking aside all of the pipework and tanks in the loft came out, only thing left in the airing cupboard is the ensuite shower pipework which we linked the hot and cold back into. It runs cold, warms up, goes Luke warm then hot n cold then grumpy friend (understandably)

 

[mikeygas]

I would always fit a pressure reducing valve on the cold water main, just after the stop tap.

This will Balance cold and hot supplies without having to take a feed off the balanced outlet on the combination valve.