Unvented Hot Water System

[Last Plumber]

Apologies, yes it’s open and on the return coil pipe

Turn boiler up a bit. It won't alter this so you'll notice but it will be better for the boiler. 65 C.

It sounded at first like there was a cross flow (cold to hot). That will have a rapid chilling effect on a cylinder but you seem to have ruled that out.

The stat works and from what I can tell, looks to be reading close enough and the valve can be heard to close when you turn the stat down, which tells me it opened.

The gate valve is open so there should be enough flow through the coil to heat the cylinder in one hour.

If the boiler is running at 60-65, then it should heat up OK.

If the flow from the boiler is being shared with something else, such as under floor heating, radiator circuits etc. Then they can in some cases rob the coil of heat. They would have to be open though and obviously will be warm/hot. You say they are off when trying to heat the cylinder? I suppose we can rule that out too?

If the flow rate through the coil is restricted in some way, you won't get the heat loss from coil to secondary (tap) water in the cylinder. That is unlikely on a new cylinder install. The honeywell valve looks to be the right way round and pipes are 22mm.

No water running through tundish (back right black thing with opening in)?

Thinking out loud as well as clutching at straws. The frustrating thing is that I know it's something that would be diagnosed on site and probably fairly easily too.

 

[Last Plumber]

When you said that the secondary return went cold?
It will do for a short time if it has been off or closed. Once the water has circulated though (minute or so), it should get warmer. Normally you would expect it to be coming back around 50 C if the outgoing was 60 C. In your case I would expect it to be around body temp?

 

[Racheal1256]

Turn boiler up a bit. It won't alter this so you'll notice but it will be better for the boiler. 65 C.

It sounded at first like there was a cross flow (cold to hot). That will have a rapid chilling effect on a cylinder but you seem to have ruled that out.

The stat works and from what I can tell, looks to be reading close enough and the valve can be heard to close when you turn the stat down, which tells me it opened.

The gate valve is open so there should be enough flow through the coil to heat the cylinder in one hour.

If the boiler is running at 60-65, then it should heat up OK.

If the flow from the boiler is being shared with something else, such as under floor heating, radiator circuits etc. Then they can in some cases rob the coil of heat. They would have to be open though and obviously will be warm/hot. You say they are off when trying to heat the cylinder? I suppose we can rule that out too?

If the flow rate through the coil is restricted in some way, you won't get the heat loss from coil to secondary (tap) water in the cylinder. That is unlikely on a new cylinder install. The honeywell valve looks to be the right way round and pipes are 22mm.

No water running through tundish (back right black thing with opening in)?

Thinking out loud as well as clutching at straws. The frustrating thing is that I know it's something that would be diagnosed on site and probably fairly easily too.

So I do have UFH both upstairs and down, no radiators. Today I have turned the thermostat down on all floor, they are mostly off anyway.
My original problem (in summer heatwave) was when I turned the floors off, the house was being warmed up as the via the HW as HW would travel to both upstairs and downstairs manifolds before being told no HW was required for floors just taps! Eventually the builder agreed to get additional valves installed and now the pipes at the manifold do not get hot when HW is needed and solved my problem…so I thought.
How exactly can I test if something is robbing the heat supply?

Currently the water coming out my taps is hotter than normal but that’s down to the boiler being on constantly all day.
I’ve now set this back to timed (2hours morning and evening) and over the next couple of days it will slowly loose heat until day 2/3 when it isn’t even hot enough for my 3 year olds bath!

Tundish is dry.

 

[Racheal1256]

When you said that the secondary return went cold?
It will do for a short time if it has been off or closed. Once the water has circulated though (minute or so), it should get warmer. Normally you would expect it to be coming back around 50 C if the outgoing was 60 C. In your case I would expect it to be around body temp?

Didn’t see this question, sorry.
I’m lost as to where in the thread the secondary went cold happened!
I still have the brass valve below the secondary pump turned off, should I turn this back open and see what happens? The timer switch for this is also off at the wall

 

[Last Plumber]

I’m lost as to where in the thread the secondary went cold happened!

Post 36.
You said it was hot when the valve was closed but went cold when you opened it.
That pipe should be cooler than the outlet? not cold though?

 

[Racheal1256]

Post 36.
You said it was hot when the valve was closed but went cold when you opened it.
That pipe should be cooler than the outlet? not cold though?

I’ve turned so many things on and off I can’t remember!
I’ve just opened this

Post 36.
You said it was hot when the valve was closed but went cold when you opened it.
That pipe should be cooler than the outlet? not cold though?

yes that was cold, it’s warm now though. Could that be because the boiler has been on all day?

 

[Last Plumber]

I’ve turned so many things on and off I can’t remember!
I’ve just opened this

yes that was cold, it’s warm now though. Could that be because the boiler has been on all day?

No it won't be why the boiler is on all day.
I think you need a Plumber who is experienced with hot water systems or a heating engineer.