Effect of replacing 22mm copper with 15 plastic

[MrGatch]

How many radiators on the changed pipe?

There are 9 rads above over two floors. 3 of the rads are towel radiators (which oddly never seem to have a problem getting warm).

 

[Riley]

SO who planned the new layout?

 

[Old Account]

Having a brand new water main fitted in 25mm MDPE direct off the 6" main in the street (asked for 32mm, but they said no). Am assuming this will be okay with the megaflo, but there is no way to tell. I'd be surprised if it wasn't.

The water main and gas main are both being replaced and every component on the heating/water system replaced so its impossible to know how it will behave. The only bit to stay the same is the existing pipework (22mm heating, 15mm hot/cold water) with the new hot and cold runs to the riser being in 22mm.

If I ask the builder to re-do the 5m heating stretch in 22mm plastic (which is about 25% smaller cross-section area than 22mm copper?) then I think he'd do that. He hasn't quoted for 10m+ of copper pipe in his quote which means I'll end up having to pay for it. No problem paying this unless the heat difference between the 22mm plastic/copper is marginal - definitely not cutting corners.

I did wonder whether the capability of the pump in the old boiler might have some input into the temperature of the upstairs rads.

I always thought that upgradinjg mains water supply needs to be signed off and certified? it also hast to be well insulated and installed at least 750mm below floor level

 

[Riley]

It does mate but they can dig the trench and run everything up to the connection in the street

 

[Old Account]

It does mate but they can dig the trench and run everything up to the connection in the street

alright, i would have thought so. normally its very expensive if thr water board does it

 

[Riley]

Had to do 6 of them in one property recently

 

[MrGatch]

I always thought that upgradinjg mains water supply needs to be signed off and certified? it also hast to be well insulated and installed at least 750mm below floor level

The water board are inspecting and connecting at the street, and yes its a 750mm trench insulated as it enters the house through the foundation. Builder is doing all that for me.

SO who planned the new layout?

There isn't a new layout really. All of the new extension space is UFH (using VarioTherm). The extent of the works means a lot of localised pipe re-routing which is where my problem comes in. I can't do much about any of the existing heating pipework except to try to maintain appropriate sized feeds as it dissapears into the ceiling void.

 

[Riley]

What I’m trying to say though is that if you have radiators not warming correctly now then it’s the prime time to correctly design your system that will have to deal with a greater workload following the extension.

 

[MrGatch]

Thanks for the all of the replies so far.

I've requested pressure and flow data from the water board who have said they will make enquiries and get back to me.

What I’m trying to say though is that if you have radiators not warming correctly now then it’s the prime time to correctly design your system that will have to deal with a greater workload following the extension.

Sounds like good advice.

A couple of the old rads have historically not heated up well on the top floor. The system was completely drained to re-route the pipework and that can't have been done in years (I moved in a year ago). Most of the rads in the house are 40 years old minimum and the bleed valves don't seem to be working which means there is now air all over the system that is proving difficult to shift. Randomly though, highest radiator (a towel rail) is mega hot.

Builder thinks as a separate issue I should replace some/all of the older radiators for more efficient modern versions. I am wondering whether very old rads are contributing to the problem? Certainly I don't have any issues with the newer towel rails.

Another issue I currently have is that there doesn't seem to be sufficient expansion capacity on the system - its a Worcester 37kW combi supplying a lot of radiators without any external expansion vessel outside of the small one I assume is in the boiler, so it will randomly dump water out of the pressure relief valve dropping the pressure to around 1 bar which then means that the water struggles to get to the top floor. New system will sort out that one though, but unsure that this situation isn't also contributing.

• Would replacing very old radiators potentially help?
• Would a badly fitted combi with insufficient expansion capacity contribute to this issue?
• Would a flushed-out system and new boiler potentially alleviate some of the symptoms?
• Could a lot of this be fixed if I just got the heating engineer to balance the system?

Really appreciate all of the advice!

 

[ShaunCorbs]

how many rads do you have totally ish?

and yes its best to replace any old rads when your redesigning the system

get the rooms individually heat lossed plus 10% and then size your rads on this

also rule of thumb no more than 2 1600 x 600 kw on 15mm this is a realistic figure

also sounds like you need to size the pump correctly to pump the water up 3 floors etc