Hot water only making its way to manifold if central heating is on

[Brendan1919]

Hi, hoping one of the UFH experts can help with an unusual issue 🙂 

 

When the central heating is off and the UFH is calling for heat - the actuators open up, the boiler fires up, however the hot water feed to the ufh mixer valve is lukewarm and temperature never gets above 24 degrees going into the loops and return is 20 degrees. Therefore the floor never reaches desired heat on the thermostats.

 

However, when I fire up the central heating, the hot water feed to ufh mixer valve is red hot and and temparature reaches 45 degrees going into loops and return is 45 degrees. The floor then warms up over the next 2 hours to desired heat on the thermostats.

 

Why could this be happening? The ufh supposedly has its own feed from the boiler, so should be independent of the central heating.

 

Ive attached pics of the ufh pipe work, manifold and actuators. Also a pic of the 3 way valves for the central heating and hot water for the unvented cylinder - both set to auto and running via hive system.

[Brendan1919]

 

[Brendan1919]

[JohnMo]

Notice you only have three loops, so the likelihood of the boiler just cannot modulate low enough and it trips soon after firing up.

 

My suspicion is the following occurs

 

UFH asks for boiler to fire up, boiler pump starts and boilers fires, but there is not enough flow to take the heat away, so boiler trips very soon after.  Has a 10 min timeout, then tries again, repeat.  Uses gas but very little heat delivered.

 

Whole heating system calls for heat, but plenty of flow available to take the heat away.

 

Unless you install a buffer it may never work, as it is.   Other option is have the heating flows turned down so the heating system runs for longer and have the UFH work with the rest of the system.

[PeterW]

Plumber has wired the UFH boiler signal into the boiler direct, not to the wiring centre as a good guess. That means the boiler fires but the pump is pushing against the 3 way and it’s not fully open - when the central heating controller kicks in then it opens the 3 way valve and then the boiler fires from the mid position signal, and everything gets toasty. 
 

Without seeing it I’m guessing but it supports why the system doesn’t get warm

[Brendan1919]

Thanks both for speedy responses, really appreciated. The boiler is firing up and like you say times out and tries again. Before exploring the buffer option, how would I check if the UFH boiler signal is into the boiler direct instead of the wiring centre?

[JohnMo]

Are your room thermostats connected to the wiring centre for the UFH or the wiring centre for the boiler?  If to the UFH the boiler signal is likely from the UFH so would be ok.

 

How do you have your radiators and UFH timed to come on.  You really want them on together then no need for buffer

[Brendan1919]

The room thermostats are connected to the wiring centre for the ufh, so the actuators open up and call for heat when needed. However unless the rads are on then the hot water flow isn’t sufficient. 
 

We have ufh set to be a constant temp as primarily live in this space. The rads in rest of house just come on for an hour in the morning and for 2 hours in evening when we bath, go to bed etc.

 

Would’ve thought we could run each heating system independent of one another?
 

 

[JohnMo]

Trouble is boilers can only modulate down so far. Your UFH looks to quite small on only 3 loops. So will not have the demand to keep the boiler happy.

 

Are running the 3 ufh loops on their own thermostats, if so your engaged water circuit could be extremely small.  I would suggest you try running the UFH only with all three UFH loops open, to see if that allows the boiler to function correctly.

[Brendan1919]

Yes they all have their own thermostats, the idea was to have different heat in different zones of the floor area. So are you suggesting we set all three thermostats to the same temp and see if all three loops calling for heat will enable the boiler to fire and stay fired up to ensure the flow makes its way to the manifold?

[Temp]

I assume the UFH has never worked corectly?

 

Q1: Is it a system boiler (pump in boiler) or is there a seperate pump? If seperate does it run when only the UFH is on and calling for heat? 

 

Q2: When the CH is off and the UFH is on and calling for heat do any rads get hot (eg when they shouldn't) ? 

 

 

 

 

Edited February 28, 2023 by Temp

[Temp]

In this picture the vertical pipes obviously come from the boiler but where do they go after passing the tap off for the UFH? 

 

When it's in the not working state (CH off UFH on and calling) do these vertical pipes get hot? I know you mentioned the manifold only gets warm but what about these vertical pipes?  

 

Edited February 28, 2023 by Temp

[Nickfromwales]

6 hours ago, Brendan1919 said:

Thanks both for speedy responses, really appreciated. The boiler is firing up and like you say times out and tries again. Before exploring the buffer option, how would I check if the UFH boiler signal is into the boiler direct instead of the wiring centre?

If it wasn’t, the boiler wouldn’t fire.

 

There’s no “exploring” a buffer, just a buying one, and-a fitting one.  
The UFH won’t ever work correctly if you want it to run independently, and it’s completely reliant on buffering via the rads atm.

[Brendan1919]

5 hours ago, Temp said:

I assume the UFH has never worked corectly?

 

Q1: Is it a system boiler (pump in boiler) or is there a seperate pump? If seperate does it run when only the UFH is on and calling for heat? 

 

Q2: When the CH is off and the UFH is on and calling for heat do any rads get hot (eg when they shouldn't) ? 

 

 

 

 

Hi, thanks for the replies.

 

The UFH probably has never worked properly as only just noticed now having to keep an eye on bills. Observed when only trying to heat floor and leave rads off in winter.

 

Q1 response - The pump is in the boiler.

 

Q2 response - The radiator on the landing, next to the airing cupboard with unvented cylindar and switches does get warm when UFH is on and CH is off. 

[Brendan1919]

5 hours ago, Temp said:

In this picture the vertical pipes obviously come from the boiler but where do they go after passing the tap off for the UFH? 

 

When it's in the not working state (CH off UFH on and calling) do these vertical pipes get hot? I know you mentioned the manifold only gets warm but what about these vertical pipes?  

 

In the pic the pipes are directly under the airing cupboard and switches for CH and HW. The boiler is in the garage behind the wall where the manifold is positioned. 
 

When it’s in not working state the hot water pipe (left hand side) is luke warm. When I switch central heating in it gets red hot. At first it is hot from ceiling to the pass off to the UFH. And they remain cooler beyond the pass off to the floor. After an hour they are hot. 
 

I’ve also observed when it’s in not working state the pipes in and around the switches in the airing cupboard are always hot. It’s as if the hot water gets to the switches and stop, trickle trickle through. Then fully pass through when central heating is on.

[Temp]

1 hour ago, Brendan1919 said:

I’ve also observed when it’s in not working state the pipes in and around the switches in the airing cupboard are always hot. It’s as if the hot water gets to the switches and stop, trickle trickle through. Then fully pass through when central heating is on.

 

I think this points to what @PeterW suggested. Nothing opening the valve when only UFH is calling for heat.

 

23 hours ago, PeterW said:

Plumber has wired the UFH boiler signal into the boiler direct, not to the wiring centre as a good guess. That means the boiler fires but the pump is pushing against the 3 way and it’s not fully open - when the central heating controller kicks in then it opens the 3 way valve and then the boiler fires from the mid position signal, and everything gets toasty. 
 

Without seeing it I’m guessing but it supports why the system doesn’t get warm

 

I'd get someone to look at it. Make sure they know its never really worked and show them the above.