Hot water dominating central heating?

[dboi10]

Hi all,

Have just had a new Ideal Vogue Max 26 system boiler installed (s plan) - along with 9 new vertical rads downstairs, new 15mm supply pipes, new Stelflow tank - its connected to 4 old rads upstairs (2 TRV, 2 non TRV).

Having a tricky time balancing the new system, but most rads are now heating up equally. The issue i'm facing is that when the hot water is turned on at the same time as the central heating, the rads start cooling (starting with those furthest away). When the hot water is turned off - all rads get hot again. Is this normal? If not, any tips? I've checked the 2 diverter valves and both are operating normally from a visual inspection.

Thanks for any help!

 

[Chalked]

Sound like your pipework to the rads is undersized

 

[centralheatking]

Hi all,

Have just had a new Ideal Vogue Max 26 system boiler installed (s plan) - along with 9 new vertical rads downstairs, new 15mm supply pipes, new Stelflow tank - its connected to 4 old rads upstairs (2 TRV, 2 non TRV).

Having a tricky time balancing the new system, but most rads are now heating up equally. The issue i'm facing is that when the hot water is turned on at the same time as the central heating, the rads start cooling (starting with those furthest away). When the hot water is turned off - all rads get hot again. Is this normal? If not, any tips? I've checked the 2 diverter valves and both are operating normally from a visual inspection.

Thanks for any help!

refer right back to your gsr installer, all this stuff is down to the fitters. It must have been signed off by law. centralheatking....if its a micky mouse installer of course we will assist it happens on here more often than you might imagine

 

[dboi10]

refer right back to your 'Registered Professional Gas Engineer' installer, all this stuff is down to the fitters. It must have been signed off by law. centralheatking....if its a micky mouse installer of course we will assist it happens on here more often than you might imagine

Agreed - however, I get the feeling I've reached the level of my installers knowledge base... I'm exploring whether i can identify the issue and help things more forward a bit quicker (with him doing the work of course). Installer thinks adding a valve to 'slow down' the pipe flow to the cylinder might be the next step - sound logical? The pipe to the cylinder is 22mm, the pipe to the rads is 15mm, so i guess it makes sense that the water would take the easiest route? (more than happy to be educated here.. haha)

 

[ShaunCorbs]

Pipe to the rads need to be 22mm main branch then tee off this in 15mm to each rad

 

[dboi10]

Pipe to the rads need to be 22mm main branch then tee off this in 15mm to each rad

pipes had to be 15mm due to floor constraints - not ideal i know - but cant be changed.

 

[ShaunCorbs]

pipes had to be 15mm due to floor constraints - not ideal i know - but cant be changed.

Change the pipes to the cylinder to 15mm

Water will always take the easiest route

 

[SJB060685]

I was going to suggest about balancing HW coil with valve earlier but held back. Though this is an option it will as intended reduce the flow but will also do so when HW only is demanded, meaning longer recovery time. Like you said the water will take the path of least resistance and in this case is starving the CH when both calling for. I think like these guys above have said the cause is down to improper rad pipe sizing.

 

[dboi10]

Thanks for all the input so far - appreciated lots. I'm thinking the two main options are A-add valve to HW coil, increasing HW heating time, balance system and hope it works, or B-rip up screed/concrete floor and lay 22mm pipe instead and do it properly (we haven't yet put our final floor down so we could still do that with some but not total disruption). thoughts?

 

[ShaunCorbs]

Do it proper while you have the chance

 

[SJB060685]

If a jobs worth doing it's worth doing properly. Remember you're future proofing your property

 

[Jones82]

Is there a gate valve on the cylinder return? I usually fit one to aid in balancing the coil with the radiator circuit. If its close to the pump you have to have it 3/4 closed or thereabouts

Surely its not 15mm to all 9 radiators from the pump?

 

[Stu-B]

If you chose to undersize the pipework to the rads then why not Heat the hot water in the small hours before the ch comes on or when you’re out at work etc... how big is the cylinder and how much are you using?

 

[dboi10]

If you chose to undersize the pipework to the rads then why not Heat the hot water in the small hours before the ch comes on or when you’re out at work etc... how big is the cylinder and how much are you using?

Good idea, but i think a brand new system, such as this, should be good enough to not worry about timing in such a picky way (plus i've a NEST which makes timing tricky)

it's a 250L cylinder, use it for a few showers per day only.
[automerge]1575586023[/automerge]

Is there a gate valve on the cylinder return? I usually fit one to aid in balancing the coil with the radiator circuit. If its close to the pump you have to have it 3/4 closed or thereabouts

Surely its not 15mm to all 9 radiators from the pump?

No gate valve unfortunately :-( - i see how much sense it makes.

Yes, its 15mm to 9 rads, over about 15m length... as im learning, not good!

 

[Chuck]

The issue i'm facing is that when the hot water is turned on at the same time as the central heating, the rads start cooling (starting with those furthest away). When the hot water is turned off - all rads get hot again. Is this normal?

It's normal for this type of system, the cylinder will have a ca 22kW heat exchanger and you have a 26 kW boiler. So, when the DHW is heating there's not much left for the radiators. The normal way to manage this issue is to programme the DHW to heat the tank at night, say from 0500 to 0700. Limiting the flow to the cylinder heat exchanger with a lock shield will reduce the peak power absorbed by the cylinder at the expense of reheat time.

 

[king of pipes]

As chuck has said program the hotwater heating times to come on earlier than the main heating and not both together you may get away with it ?, I have a job to sort out Monday with exactly the same issue vertical rads all piped off 15 mm the carrying capacity of 15mm pipe is just not enough to supply these rads and it's a 37kw valliant eco tec system boiler so is correctly sized just badly installed I am increasing to 22 mm as far as I can from the boiler to the rads so will post a few pictures next week . Kop

 

[SJB060685]

As chuck has said and what I forgot to mention is modern day cylinders are far better at transferring heat than the old foam lagged copper cylinders. If the cylinder for example has a 22KW coil and your boiler is 28KW then most of your generated heat is consumed by the cylinder leaving very little for CH and if the coil has a larger rating than the boiler then obviously it will only heat at boiler capacity. You can see this information on data sheets of appliances.

 

[dboi10]

Thanks for all the advice and info. Over the weekend I dug up and took out the 15mm main run and replaced with 22mm (had to lower the level of the chase in the floor into the foundation concrete!), switched on this morning, all rads very hot, not even balanced yet... amazing.

Any advice for what to put into the floor chases? Previously covered in self levelling compound. Seems to have worked well- but is expensive. (and i understand & accept the dangers of putting pipes in a solid floor).

 

[king of pipes]

Really should be lagged then back filled with sand and topped up with sharpe sand and cement mix and floated off level . Kop