Should I be pressurising my central heating system?

[Clara1989]

Hi All, getting confused by plumbers so I'm hoping for some advice from some of you who have been through this before.

I currently have a system boiler that does the heating and heats an old vented copper tank in the attic fed by a cold water tank (converted attic so it doesn't get cold). The cold tank has 2 shower pumps (both now broken) off it. My mains pressure is around 18-20 litres per minute.

1. Currently getting prices to move to an unvented tank so I can get rid of the shower pumps = less noise and future breaks....? is this the right thing to do? we moved into the house 6 months ago and plan to be here long term.

1. 2/3 plumbers have said they will pressurise our central heating at the same time. stating benefits of less air in the system. The 3rd plumber has warned us against it as potentially causing issues with joint leaks - he doesn't think the benefits are worth it. Thoughts?

P.s we currently have very noisy pipes when the central heating is warming up and when hot water goes to the main bathroom. Could I assume a pressurised system might help reduce this?

p.s.s what did you pay for changing from an vented to unvented tank?

Thanks for the help!

It's hard to say. If you move to an unvented cylinder then you will increase pressure in the hot water supply, so there is a chance you will get more pipe banging and noises. And obviously the increased pressure may lead to leaks.

If you pressurise the hot water heating loop there are the same potential issues. Although I think (not sure) the potential for pipe knocking is probably not so bad in this loop. But certainly if you pressurise it the potential for leaks is higher as it will have been operating for years at ambient and now you will try to shove 2-3 bar through it with a pressurised system.

I really like unvented systems, but not sure whether taking unpressurised older systems and turning them into unvented is a good idea. If I was going to do something like that I would be thinking about budgeting for some extra work in case leaks appeared. The accessability of the pipework is also a consideration. In some houses all the pipework is easy to get to, but in newer ones it can all be hidden.

You might find that simply replacing the pumps every 5 years is cheaper than installing new systems. Look for the dB rating on the pumps to try to get something quieter. If you google quiet shower pumps you might find stuff 20-30 dB down on what you have currently. Which is a lot if you add in other stuff like anti vibration.

Thanks for this, ahhh indecision. The current tank isnt really doing the job at the moment. We run out of hot water even when we have it set on as we know lots is about to be used. Sounds like you might be recommending just changing the tank to a larger modern one and some new pumps? Not sure we could fit a larger tank in the space though unless the cold water feed tank was removed. Its a lot of money to potentially have leaks everywhere - sure the house is cursed so I'd be expecting it!

If you are running out of hot water with a vented cylinder if you replace it with a unvented one of the same size you will probably have exactly the same problem in terms of water temperature/ total hot water available.

Have you tried increasing the temperature of the heating loop at the boiler ? Or increasing the trip temperature on the cylinder so the water in the cylinder is hotter ? This way you will need less hot water to mix down to shower temperature as it will be at a higher temperature.

If you do this your CH will be less efficient though. Probably. You can probably compensate for the increased radiator temperatures if you have TRVs on the radiators to turn down.

My 135l hot water tank does for 2 showers. What is your tank capacity.

Thanks, Yes temperature raised up to 75 to try get the most out of it. We would be replacing it with a larger tank - we can fit a larger unvented one in, as the cold water tank that's directly above it would be removed. Think the current one is 120ltrs but we do the washing up/have showers/run little one a bath in the same hours. So peak demand is quite high and the tank doesnt seem to warm up to fast

My 135l tank takes about 30 minutes to warm up.

I can see how your instantaneous water demand is pretty high if you try to run baths and shower twice all in a short time period. So your choices can be either to spend a lot of money re-jigging the system and getting a bigger tank. Or you can change your lifestyle to suit which would be a lot cheaper. A £300 spend on a dishwasher might save you some water (maybe 10l or so) and time if you have room and represent better value than money spent on an upgraded tank. Another thing you could do is make sure you use a lower flow rate on the showers. It could be that with the pumps you are absolutely blasting water out of the showers. Although a lot of people like that, there is a price to be paid for it.

Three more things that might make a difference, make sure the CH is off when you are heating the hot water. This might mean more energy goes into the hot water. The other is obviously heat the hot water so it gets to max temp before you start using it, although I am sure you are already doing this. The final thing might be to switch around the order in which you do things if you can.

I guess it is all about whether you want to spend the money on upgrades or are willing to switch around trying to optimise use of your existing system.

Obviously the worst outcome is to spend a load of cash and not actually get any improvement.