Advice needed - 10mm system conversion?

[doitmyself]

you can upgrade to 15mm and it will give increased flow to the rads.

You don't need increased flow; you need the correct flow, which is determined by the rad output and the required temperature drop.

Yours being open vented at the moment would be better with 15mm as this would help prevent the black sludge from blocking the pipes.

But a 15mm pipe will have a lower water velocity (metres/sec) than a 10mm (for the same flow rate), so there is more likelihood that sludge will block the pipes, particularly of there are long horizontal runs. A 10mm pipe can carry 2.5kW at an 11C drop and 4.5kW with a 20C drop.

 

[Jimbobber]

Combination boilers serve a purpose a bit like an electric shower (when needs must), good for a flat or a small 2 bed house maybe.

But the carcass will be in 15mm pipe for a start. Unvented cylinder will be at least 22mm distribution and larger for a big property.

Also a combination boiler doesn't give you full mains flow rate, there is a reduction as to be expected. Running a shower off of a combi ? Um yeah lovely system:uhoh2:

We fit combi's in a lot in new builds sometimes in quite large property's running one shower and the rest electric, but remember just because big building companies are specifying this doesn't make it good practice, it's just profitable haha

 

[1animal1]

I'm by no means an expert as you've probably guessed. But I have done a lot of reading on this and apparently the unvented gives you the same hot water pressure no matter how many taps are running, combis simply cannot do this, I've experienced a large combi and as good as it was.... It could not handle more than two hot taps at once without a significant pressure drop.

Diy, are you saying I'm likely to get the same drop with an unvented?

 

[Jimbobber]

1animal1 you're barking up the wrong tree listening to Mr Diy, he clearly doesn't do this for a living. An unvented cylinder will easily outperform a combi.

What system you size and spec will depend on your intended usage and size of your house etc. Eg if you had a very big house, you could have say a 350ltr cylinder and distribute in 28mm pipe. For your more average 3 or 4 bed house distribute in 22mm pipe with a 200-250ltr cylinder. If you've got good mains pressure it's all good 😛unk:

 

[Ermintrude]

AFaiy

 

[cr0ft]

Both systems rely on the mains pressure to push the water out of the tap. The only difference is that the unvented cylinder acts as source of hot water in the path between the mains input and the tap, so the water does not have to be heated instantaneously.

If you have five litres/min from the mains, you will get five litres/min coming out of the tap irrespective of which system you have.

Pressure and flow rate are not the same thing.

But if you have 50L/min from the mains you will only get a maximum of around 15/16L/min (in Summer, in ideal conditions) from the best combi boilers on the market. The unvented cylinder will give you 50L/min. That is why mains pressure and flow rate must be checked before fitting either of these products. Dynamic pressure thus also tends to be far better on unvented systems compared to combi boiler systems.

With a combi boiler the hot water to the whole house should ideally be supplied in 15mm pipework. This massively limits the flow rate to the taps as well and causes much larger pressure drops through the system than an unvented setup which will be run in 22mm for significant chunks of the pipe run.

I know you don't directly infer it but lets not try and compare combi boilers to unvented cylinders. An unvented cylinder is a far, far superior solution in terms of hot water performance (assuming the mains is good enough to justify fitting one).

Of course it comes with a far, far superior cost too compared to a combi boiler!

 

[1animal1]

That ties in with most of what I've read Bob... The downside I'd read was the complicated nature of the system.

I've had a right evening - drained down the system by removing a downstairs rad, then had to mock up a tap to one of the valves as it was leaking, using push fit, a stopcock and a spare piece of pipe.

Then attempted the gate valve on the pump, what a job! Couldn't get it off to start with then found myself removing the pump to get it out. The pump was so heavily gunked it was ridiculous! I then spent over an hour trying to free up the pumps channels whilst trying to make sure I left no sludge to later block my 10mm pipes. Anyway, the lower gate valve compression joint was too close to a collar so I couldn't get to the old olive and had to refit it with the old compression olive/nut (squeeky bum time), not least as it looked like someone else had attempted to remove it and bent the 22mm pipe out of shape - total gamble when refitting. Luckily I'd bought some jointing compound.... The lower seal was perished so obviously replaced that along with the valve, refilled the system and all is good in the world again! One question though, after bleeding the radiators, can I switch back on the hot water or do I need to bleed anywhere else in the system? I started the pump up briefly and it made a gurgle for a minute then started working, I stopped it however to post up here before going any further.

The other joint on the bottom of the cylinder I attacked with the wire brush, still not clean and full of white crusty stuff. I think I've found the leak though, on the 2nd 90, dry joint possibly due perhaps to the hard to reach location. That'll be a plumber job I think....unless I can cut the 22mm pipe 2 inch from the cylinder and mock up some 22mm push fit bends? Is this dooable?

Assuming after testing that the hot water works fine, tomorrow I'll drain it down again and fit the drain tap valve to one of the lower rads.

Can anyone help regards the question on refilling the system before I attempt to use the hot water?

 

[village idiot]

If you have an Immersion on the cylinder, then you can just switch that and use while the heating side is drained down.
If not, then you need to refil the heating system before you use the hot water. After refilling the heating system, you need to bleed the pump by undoing the big screw till water escapes then tighten back screw. As for draining the system in future, you can fit one of these. If all downstairs rads are drop downs, then fit one to everyone of the rads.
Angled Radiator Valve & Drain Off 15mm x ½" | Manual Valves | NoLinkingToThis

 

[1animal1]

Thanks village. I've got one of those to fit tomorrow, I just wanted to fill the system back up to check the joints I'd attacked first. I had already released that screw and water flowed almost immediately so presume it's good to go. Gonna warm it up and check shortly.

What do you think about the dry joint, is it worth attempting speed fit given the horrible access? My concern is the proximity to the boiler after reading not to use steed fit within 1m of a boiler. Also is there any detriment to undoing the bolt to the cylinder that holds that pipe in... I could do with removing that pipe to clean before sliding any speed fit on

 

[1animal1]

This is the joint. I assume it's a standard 22mm compression which will probably need a new piece of copper 22mm. I may buy one of those and a couple of 90 speed fits to hit the pipe disappearing into the floor. Can anyone see an issue with this

 

[cr0ft]

A plumber with a pipe freezer and a tool like a Fein should have that replaced within an hour or two at most. Slice the pipe once frozen on both sides of the coil, drain water out between ice plugs and solder a nice bit of new copper onto a mew cylinder connector to boot. No pipe freezer and add another hour onto that for faffing about draining and filling the system to do the job.

 

[1animal1]

What would that cost be roughly croft? I'm eager not spend given we've just moved in and have a million other things to buy. However if you think it's worth getting a plumber in? I'm probably only looking at a couple years use before it's replaced. Cost of 22mm pipe and fittings comes in at £15 for me to do

 

[doitmyself]

Diy, are you saying I'm likely to get the same drop with an unvented?

No, far from it. I was not suggesting that a combi is superior to an unvented but that, if you are having problems supplying two outlets at the same time with a combi, you will probably have the same problem with an unvented. This is because the incoming flow and pressure determines what comes out.

As for ShaunCorbs unasked question why an unvented can do two baths while a combi can't, the brief answer is: because the water is not heated instantaneously.

 

[1animal1]

Thanks doitmyself, and yes I agree that the cold water will reduce the more sources request, but as you quite rightly say, the hot water will be less affected when compared to the combi.

I do find myself with a problem however, currently we are using the electric shower in the main bathroom because we haven't another solution. However what we do with the en suite is still entirely open... Go electric or remain on a thermostat regime - with an increased pressure to make it useable. Bearing in mind that we are considering buying solar panels, electric showers all round could be the answer despite their aesthetics.

 

[1animal1]

Croft, I'm taking your advice and getting the plumber around for this final leak. The bolt to the cylinder looks like it has an integrated piece of copper which I'd have to replace, this would then need soldering regardless which is beyond me. I'd love to learn how to do these types of joints eventually, properly.