Gas Rayburn with unvented water tank

[algo]

Hello,

I have recently moved into a property and would be very grateful for any advice on a central heating issue.

The flat currently has a gas-fired rayburn which powers the central heating and hot water. The current hot water system is a vented system with water tanks in the bathroom and a shower pump. There is however no header tank for the radiators, and the primary loop is closed and pressurised. Below is a couple of pictures of the cupboard to confirm this in case it helps at all in clarifying! (Sorry I don't know why they're on their side)

GIven that the Rayburn boiler is thermostatically controlled and is a closed-loop pressurised system, is there any reason that I couldn't use an unvented (e.g. megaflo) cylinder for the hot water?

The mains pressure is good and I know I have to test the flow rate, but the pipe from the cold water tank feeding the hot water is 22mm and is next to the where the mains water enters the property.

I have read that some boilers will not work ok with a megaflo system, but would a gas-fired Rayburn be ok? Annoyingly the existing hot water tanks are about 30cm in diameter so I'd have to think about relocation unless it's possible to get very slimline tanks, but my guess is not!

Any help much appreciated!

 

[dcawkwell]

Normally the heat exchanger in a rayburn isn't suitable for a pressurised
system. Your gas one may be.

But the unvented cylinder doesn't care. You can heat an unvented
cylinder with a seal or open vented system.

I would remove rayburn and cylinder and install a glow worm ultra power.
A cross between unvented cylinder and combi. Unvented delivery rates then
it falls back to combi should you run out of hot water. It will
also operate in just combi mode for economy.

 

[algo]

Hello!

thanks very much for the reply - much appreciated. My other half loves the Rayburn - I think she'd divorce me if I got rid of it! I will definitely bear your suggestion in mind though - sounds great.

Part of the motivation is to get rid of the cold water tanks in the bathroom which are a pain as they really lower the ceiling and I keep nearly banging my head.

Thanks again for the advice - I'm hoping the gas boiler part of the rayburn is ok since I think it is currently a pressurised system... it looks that way from the pump and pressure vessel in the photos, but I'm no expert! I wonder if an indirect combination thermal store would be a better option.

Thanks again

 

[mysteryman]

You need to check which Rayburn it is. Some of them have completely independent boilers which can be pressurised - these also have full boiler control and don't need a heat leak. This should be checked, as it could be wrong, I'm not saying it is wrong, mind you. Stay with the Rayburn by all means if you wish. Don't have a thermal store, they only benefit the manufacturers of thermal stores. This may cause a few comments from their enthusiasts, but I would ignore that.

 

[Agile]

Unvented cylinders need to be installed by a qualified person who will check that the boiler is suitable.

As far as I am aware there are not any thin unvented cylinders available. Most are quite fat and many based on a 505 mm diameter.

Tony

 

[Dan Robinson]

Albion/Range, Megaflo, and a few others make slimline unvented cylinders.

 

[algo]

Hello,

and thanks for all the replies - really useful. I have spoken to some qualified people to fit unvented systems, and have some conflicting opinions about the Rayburn which is why I'm asking on here too. As it currently a pressurised system it seems that it will be ok, but I want to be doubly sure before I go to the expense of installing an unvented cylinder.

I will take pictures of the Rayburn and the technical bit inside the door, and hopefully that will help - I should have done this before. Will post up later.

Many thanks again for the advice

 

[Dan Robinson]

The point is - it makes no difference whether your primary side is sealed or not as to whether you can have an unvented cylinder.

It is a separate issue entirely, and the only place you will get a definitive answer is Rayburn themselves.

 

[algo]

Thanks again,

I've understood that now. Trying to get answers for the Rayburn is tricky as it's the GD80 - superceded as the 380G, made in 1992 and now no longer technically supported. It has twin gas boilers - one for the cooker and one for the water primary loop. Here's a picture of the schematic of my setup:

I'll try again tomorrow to get some definitive advice from Rayburn/AGA, but for the modern rayburns it looks promising as it states here that unvented cylinders can be used:

http://www.rayburn-web.co.uk/raytech/dhw6.htm

Many thanks to everyone who's helped so far. I'll post up what I find out and do once I've verified for sure it's ok.

 

[Agile]

Whilst you say you will get a qualified person its worrying me that you are posting a pipework plan.

That plan you have shown CANNOT be used with an unvented cylinder!!!

At least not safely and in accordance with the regulations.

I dont understand why you are posting that if you really plan to have a qualified installer. It makes me wonder if you are planning an illegal DIY job!

Tony

 

[algo]

Hello Tony,

I assure you I'm not going to do anything of the such. The plan is from the literature I found from the flat. I'm just trying to understand for myself, but I wouldn't be so stupid as to try and do this myself. I only posted the plan because I thought it might clarify what the pictures are. I have spoken to two qualified plumbers, experienced in installing unvented systems and with Rayburns and have got conflicting information which is why I'm trying to understand.

If the plan shows it cannot be used with an unvented cylinder, then that's that - I'll live with the cold water tanks in the bathroom. Could you explain why the plan makes it clear it's not suitable for an unvented system?

Of course the heating engineers I spoke to explained about the extra safety features they have to install, pressure release etc, required for an unvented cylinder - I'm about to have a child and am under some pressure to get the new flat ready which is why the necessity for expert advice, especially as I am aware than if it wasn't done properly it would literally be a ticking bomb.

Many thanks

Ewen

 

[mysteryman]

Ewen, as far as I remember the GD80 has a low water content boiler, and it was a fairly good model. That being so, your sealed heating system should be OK, and the type of cylinder, vented or unvented, makes no difference to the Rayburn. Can you achieve the same objective by raising the cold storage tank somewhere else in the house, and keeping the existing cylinders?

 

[algo]

Thanks mysteryman,

it's a ground floor flat I'm afraid - so the tanks can only sit high in the bath room - it's a bit of a pain. If I had a loft this wouldn't be a problem! Hence the need for a shower pump currently.

Will ring Rayburn tomorrow and ask them for sure but thanks a lot for your encouragement.

Ewen

 

[Agile]

You seem to be focussing on the Rayburn. Thats only a heat source.

What is required is to correctly connect it to an unvented cylinder.

Anyone qualified to fit unventeds should know what to do.

The diagram you posted is how to connect a vented cylinder. Thats a completely different method of connection.

Before choosing an unvented cylinder the dynamic mains flow rate needs to be measured.

Tony

 

[algo]

Hi Tony,

thanks again for the reply. I am precisely focussing on the Rayburn because as had been mentioned already on this thread, I need to be certain the boiler is up to the job, and there is some uncertainty about this. I am having difficulty getting hold of Rayburn to ask them which is why I am asking here.

The actual work will be done by a certified engineer experienced in doing this installation - the details of which I trust him on, so I'm not worrying about that here.

Thanks a lot for your time

Ewen