Thinking of going for an unvented cylinder...

[TheKeymeister]

I'm doing some work in the loft and need to relocate or get rid of the cisterns for hot water and central heating. Hopefully converting the central heating to be a sealed system won't be a problem, the boiler can handle it, and I'll wet pressure test it when I alter some pipework next month to see if it's up to it first.

I've been thinking of an unvented cylinder for a while when the current one goes bang to get better pressure on the hot side of things, but now I'm thinking why not just get one fitted now to kill two birds with one stone and ditch the loft tank. Ideally I would like to locate the new cylinder in the garage next to the boiler, so no issues with floor loading or leaks, and it will free up the airing cupboard upstairs giving us some much needed storage space.

I've got absolutely no plans on attempting to fit an unvented cylinder myself as I understand the dangers of one fitted incorrectly. I've been doing some reading and I've just got a few questions to hopefully decide whether I go for it or not...

1- Can the pressure relief valve be piped to discharge onto the path directly outside the garage, or does it have to go into a proper drain? It'd be possible for it to go through the wall at low level to minimise the risk of injury etc. There's a drain pipe in the path but no gulley, I could put one in if required but don't want to start digging holes if I don't have to.

2- My house is a 4 bed detached, 1 main bathroom and an en suite with a shower, from what I've read a 210 litre cylinder is roughly what's needed, but my existing cylinder looks tiny in comparison (see below). Currently the hot water is programmed on for an hour in the morning and an hour at night which is more than enough for what we use. Do I really need a 210 litre, will a smaller one be cheaper to run? I'm not worried about the purchase price difference as it's not that much really.


3- In the en suite I've currently got a Triton thermostatic power shower (has hot and cold feed, doesn't heat its own water). It'd be a major event to get rid of this and revert to a normal shower, is it likely to run properly whilst under mains (ish) pressure hot and cold water? I'm thinking of fitting a steam shower in the future, but not quite ready for it yet as it'd involve smashing the en suite to pieces.

Thanks in advance for any advice...

 

[dilalio]

Before you toy with this plan any further...

Check your incoming mains working pressure and flow.

 

[Mottie]

That's almost what we've had done. We got several quotes from different plumbers and they all tested the water flow/pressure when they came to give the quotes.
We got rid of the cold water and central heating header tanks from the loft. I was going to have the cylinder fitted in the loft to gain a cupboard but in the end we left it where it was as my wife wanted to keep the airing cupboard. We have a 150 litre tank in a 3 bed, one bath house but there's only the two of us. I'm sure the old tank was smaller (130 ish) but the pressure in the shower now - wow! Trouble is, now that it's more powerful, it don't half empty the hot water tank quicker and a 150 is about as small as I would like to go. I always leave our hot water permanently on, the new cylinder is so well insulated it doesn't lose much heat at all so I think you are really only heating what you have used. One good, long shower or bath and it's all gone. If someone else wants to have a shower or bath straight after it's not a problem whereas it would be if it was before the hot water was due to come on again.

Our heating was converted to a sealed system at the same time too and our pressure relief pipes for the heating and hot water systems are vented through the flank wall to our side alley, not into any drain. I think it's only condensate that has to be discharged into a drain.

The old cold feed from the tank in the loft was converted to mains pressure at the same time so that the feed to our shower and basin/bath taps was balanced. Could you not just disconnect the power shower from the mains electricity supply and let it work under the mains pressure hot and cold feed or does it need power to allow water to pass through?

 

[TheKeymeister]

Thanks for the replies.

Yes, I should get the mains pressure and flow tested, I'll get this done when I get the man in to pressure test the heating pipework. I know you shouldn't assume but it should hopefully be OK, others on the same estate have had unvented cylinders fitted, it's a 25mm MDPE feed from the street and there's a water booster station 100m away and a water tower 150m away!

That makes perfect sense about the increase in pressure/flow meaning the tank empties quicker - I never thought of that to be honest. I reckon I'll go for better looking at it than looking for it, and spec a 210L.

That's good info about the pressure relief pipes and saves me digging holes in concrete so I'm happy!

Shower has a cut off solenoid I believe so won't operate without power. I've just read the manual and it states a maximum static pressure of 1 bar, I suppose I could try pressure reducing valves to bring it down a bit as a temporary measure. Worst case I can chase a channel out at the back of the shower and drill through and fit a non powered one.

Sounds like its time to chat up my plumber mate, I've got a huge list for him now, fit unvented cylinder, convert heating to sealed, install bottled LPG feed to cooker (no mains gas round here)...

 

[muggles]

Make sure your plumber mate is G3-registered

 

[TheKeymeister]

Hopefully this means he is...

 

[hard-work]

The TheKeymeister, things have moved on. With a 25mm main pipe you look to have the flow for a mains pressure system. I don't know how old your existing boiler is and whether it is condensing or not. Combis have come a long way. Look at the Ferroli 38C, a quality product despite what the stuck in the muds may say. It delivers an impressive 16.4 litres per minute. That is enough to fill a bath at about the time you do right now. You then get a new `highly efficient` boiler, more space and no annual unvented cylinder service charge, and reduces a potential explosion (remote we know but it is there). If you go all mains pressure you will may need to replace the toilet valves and maybe some taps as they may be low pressure jobs.

You may want to keep the loft cold water tank if it takes up no space and have it feed the toilets, bath, basins and the two wet appliances in the kitchen. Spread the cold water load over the cold mains pipe and cold tank, you also have stored water backup if a main failure. If you are a shower a toilet flush will not affect the shower.

Remove the noisy power shower pump of course and have only the shower and kitchen on the hot & cold mains. Have flow regulators on the hot and cold mains pressure outlets and one on the pipe t the cold water tank set to 6 litre per minute. The regulators are cheap enough and come with an integrated isolator valve. The 38C may need a larger gas supply, or part of it uprated to 28mm from the meter. Or if there is a 22mm gas pipe already there just run another 22mm pipe from the gas meter in parallel to drop costs. The boiler is in the garage? Where is gas meter?

The great thing about this combi is that it will deliver hot water for ever. It will deliver 492 litres in 30 minutes. That is the equiv of a 500 litre cylinder. Ever seen the size of one of them? And the price?

 

[muggles]

The TheKeymeister, things have moved on. With a 25mm main pipe you look to have the flow for a mains pressure system. I don't know how old your existing boiler is and whether it is condensing or not. Combis have come a long way. Look at the Ferroli 38C, a quality product despite what the stuck in the muds may say. It delivers an impressive 16.4 litres per minute. That is enough to fill a bath at about the time you do right now. You then get a new `highly efficient` boiler, more space and no annual unvented cylinder service charge, and reduces a potential explosion (remote we know but it is there). If you go all mains pressure you will may need to replace the toilet valves and maybe some taps as they may be low pressure jobs.

You may want to keep the loft cold water tank if it takes up no space and have it feed the toilets, bath, basins and the two wet appliances in the kitchen. Spread the cold water load over the cold mains pipe and cold tank, you also have stored water backup if a main failure. If you are a shower a toilet flush will not affect the shower.

Remove the noisy power shower pump of course and have only the shower and kitchen on the hot & cold mains. Have flow regulators on the hot and cold mains pressure outlets and one on the pipe t the cold water tank set to 6 litre per minute. The regulators are cheap enough and come with an integrated isolator valve. The 38C may need a larger gas supply, or part of it uprated to 28mm from the meter. Or if there is a 22mm gas pipe already there just run another 22mm pipe from the gas meter in parallel to drop costs. The boiler is in the garage? Where is gas meter?

The great thing about this combi is that it will deliver hot water for ever. It will deliver 492 litres in 30 minutes. That is the equiv of a 500 litre cylinder. Ever seen the size of one of them? And the price?

Twaddle

 

[hard-work]

Twaddle

That you for your solid contribution to this thread.

 

[muggles]

Any time. I like to be succinct I could, however, go through your post quoting individual lines and explaining why they're twaddle if you'd like?

Incidentally, where do you get your 16.4l/min from? As far as I can see it's not a figure Ferroli quote anywhere....it's certainly not on their website or in their brochure

 

[TheKeymeister]

My boiler is a 20 year old HRM Wallstar, easy to work on and repair, and still going strong so I've got no plans to replace it.

The nearest gas meter to my boiler is approximately 5 miles away in the next village, as stated above I have no mains gas, so I reckon I would struggle with the Ferroli you suggested...

 

[Mottie]

I have a 5 metre 15mm copper pipe feeding the mains in my house. Plenty of flow and pressure although reading one of the above posts, it reminded me that I did have to replace the float valve in the downstairs WC (too much pressure) and the cartridge in the hot side of the kitchen mixer tap (dripping when converted to unvented cylinder). Cold side of tap fine after the switch from gravity to mains pressure.

 

[hard-work]

My boiler is a 20 year old HRM Wallstar, easy to work on and repair, and still going strong so I've got no plans to replace it.

The nearest gas meter to my boiler is approximately 5 miles away in the next village, as stated above I have no mains gas, so I reckon I would struggle with the Ferroli you suggested...

Ferroli make an LPG version.
https://www.plumbnation.co.uk/site/ferroli-modena-he-38c-lpg-combination-boiler-erp/
My advice still stands. If you have an oil boiler an oil combi can be used. You may find the cost is less than an unvented cylinder overall, an cheaper bills having a new high-efficiency boiler. Price it all up.

 

[hard-work]

Any time. I like to be succinct I could, however, go through your post quoting individual lines and explaining why they're twaddle if you'd like?

You can do but you will be spanked.

Incidentally, where do you get your 16.4l/min from? As far as I can see it's not a figure Ferroli quote anywhere....it's certainly not on their website or in their brochure

Look at the Ferroli 38C manual. Download it. Clearly states 16.4. The Modena only has 4 moving parts. Quality components inside.

 

[Dan Robinson]

Look at the Ferroli 38C manual. Download it. Clearly states 16.4.

Really?