Service unvented cylinder as part of annual boiler service

[Donkmeister]

I'm considering having my clanky old central heating fully-replaced in preparation for building a new bathroom. New boiler, cylinder, pump set, pipework, the lot.

Unvented cylinders are now looking competitive in terms of price. Once I factor in the cost of a decent shower-pump for gravity-fed, the unvented system appears slightly cheaper than a copper cylinder in terms of initial outlay.

However, the unvented cylinder needs servicing once a year to check it won't go pop. Logically, I might as well get this service done at the same time as the boiler service.

In your experience, does this servicing add "much" to the cost of an annual boiler service? How often do they need repairing?

If it's going to be an extra £50 or so, that sounds good to me. But, if it's going to be a £200 job every year I might stick with a copper tank!

What other experiences have you had with unvented systems? I have decent mains pressure and flow so it seems like a good idea for me, I love the idea of having a torrent in the shower with no pump noise in the airing cupboard! Plus I like the ones that have multiple inputs so I can have some panels installed on the roof later on.

EDIT: Just looked at my incoming and it's only 15mm. Can unvented be fed adequately by a skinny incomer?

 

[swbjackson]

Servicing costs should be minimal as long as you get a decent stainless steel one. Steer clear of one that's got a sacrificial anode as these need checking annually and replacing when eaten down. They are a complete pain to check and change.

Mike

 

[Donkmeister]

Thanks Mike

I live in quite a hard water area - are sacrificial anodes pre-requisite in such areas or is it just so the cylinder can be made of cheaper-grade steel?

 

[gas4you]

Cylinders such as the Megaflo and Santon are made of a high grade steel that will resist the scaling up more therefore not needing a sacrificial anode.

An annual service on a Megaflo at the same time as a boiler service would be about 30-45 mins tops, so only about an extra £30.

 

[BigBurner]

Unvented cylinders are now looking competitive in terms of price.

Don't bother get your self a high flow combi. Beats the daylights out of an unvented cylinder for DHW delivery.

It takes about 10 minutes to exhaust a 200 litre cylinder, thats is you get 20 litres/min out of the hot tap, which many cannot give. After 3/4 re-heat which takes over 20 mins, if you are lucky, and will not give 60C, well not from a coil anyhow, you are still well short of a mid flow combi. And this cylinder reheat is when all the boilers heat is being dumped into the cylinder. Have the boiler heating CH at the same time the figures are appalling.

It will take around 10 mins to dump 200 litres from an unvented cylinder, then no hot water, so another bath cannot be run in the en-suite. Then another 20 minutes to get another 150 litres. So, 350 litres in 30 minutes with a big cold water gap, compared to to 450 litres in 30 minutes uninterrupted by a 15 litres/minute mid sides combi.

Now look at a 23 litres/min combi or Rinnai multi-point. That is 690 litres in 30 minutes delivered. That is a bath after bath. How long will a 18kW boiler take to re-heat a super large and super expensive 700 litre unvented cylinder? Not to mention the extension built for it!!!

No contest. An Ethos or MAN combi, Rinnai Twinflow or multi-point p1ssess all over a cylinder in DHW delivery.

Now look at say W-Bosch 550 stored water combi, which has an integral heat bank. It delivers 25 litre/min while the store is charged. It will dump 180 litres in 3 minutes, then reverts to what the burner gives . 41.1kW is approx 17 litres/min. So, in 30 mins this will deliver 180 litres + 459 = 639 litres. All uninterupted flow. No contest in a combi vs. separate system boiler and cylinder.

A W-Bosch HighFlow 550 costs under £2,000. How much would a 650 unvented cylinder, system boiler and all the controls cost? Ermmmm, Ermmmm.

Combi wins:

1) in installation costs.
2) in space saving (seen the size of a 700 litre cylinder?)
3) in speed of installation.
4) in running costs.
5) in DHW delivery.

How come the bathroom changers can't work this out?

 

[BigBurner]

Cylinders such as the Megaflo and Santon are made of a high grade steel that will resist the scaling up

You made that up. They scale like hell in hard water areas.

An annual service on a Megaflo at the same time as a boiler service would be about 30-45 mins tops, so only about an extra £30.

£30? To test all controls on an unvented? That is a cowboy who does very little at all except bang some tools.

 

[BigBurner]

If it's going to be an extra £50 or so, that sounds good to me.

It would be as you get the money. So £50 a year by 20 is a £1,000 - at todays prices, which would rise accordingly as the years roll on. So more like £1,700 in real terms. Just for having a cylinder of hot water in your house Sound cr@p value to me.

 

[gavinda]

Cylinders such as the Megaflo and Santon are made of a high grade steel that will resist the scaling up

You made that up. They sacel like hell in hard water areas.

An annual service on a Megaflo at the same time as a boiler service would be about 30-45 mins tops, so only about an extra £30.

£30? To test all controls on an unvented? That is a cowboy who does very little at all except bang some tools.

so what tests need to be done.. im doing my uv in a couple of months... would like some advice..?

 

[giblets]

And don't forget that the guy servicing the UV would need to hold a G3 ticket.

 

[gas4you]

Cylinders such as the Megaflo and Santon are made of a high grade steel that will resist the scaling up

You made that up. They sacel like hell in hard water areas.

An annual service on a Megaflo at the same time as a boiler service would be about 30-45 mins tops, so only about an extra £30.

£30? To test all controls on an unvented? That is a cowboy who does very little at all except bang some tools.

As per usual Dr Drivel you know absolutely nothing about the real world from behind you google keyboard.

Never had a modern Megaflo or Santon scale up and I am in a very hard water area.

Come on then Dr Drivel tell us what there is that will take more than about 45 mins to service on a megaflo? (Bet you can't/don't answer this directly as per usual, but reply with some obscure comment or insult as one who has not got a clue has to resort to )

The longest part is taking apart the multi-function valve to clean the strainer.

As you are not G3 qualified, or indeed hold any qualifications that enable you to comment from a point of knowledge on any subject posted on this forum, I suggest you keep it shut, take another Sanatogen and lie down for another afternoon nap.

 

[gavinda]

[
Come on then Dr Drivel tell us what there is that will take more than about 45 mins to service on a megaflo? (Bet you can't/don't answer this directly as per usual, but reply with some obscure comment or insult as one who has not got a clue has to resort to )

no fair.


i was fishing first

 

[Donkmeister]

I have seriously considered a combi, but when I did the maths and thought about overall system reliability a combi doesn't stack up for me...

I would like around 20 litres a minute from the shower. I want that in all weathers, so let's assume the incoming temperature is 0 celsius and the showerhead temp is 40 celsius.

The power required to raise 20 litres a minute by 40 celsius is 56kW. I've seen plenty of combis in the 30-38kW range, but that will only give me 12 litres a minute or so. That's not a bad shower, but that's 15+ minutes to fill a bath and it rules out a coliander head or bodyjets in winter.

With a 200 litre cylinder at 60 celsius, and an incoming temperature of 0 celsius I can have that 40 celsius shower at 20 litres a minute for 15 minutes. 300 litres of water in all.

Additionally, I'd like the option to add alternate heat sources in future. I'd like to be able to have that 300 litre shower with less guilt! Finally, all boilers break down, but at least with a cylinder I'll have an immersion as back-up and can employ the services of a more leisurely repairman rather than a 24 hour emergency plumber!

 

[mickyg]

I live in one of the hardest water areas in the UK, I also operate in probably THE hardest water area in the UK close to me. I have never come across a good quality UV cylinder scaled up. Copper ones die quickly and Aristons I've had leak aswell(scale or not? ) but no megaflos, santons, vaillant, range etc.... and we have whole estates of them. Biggest problem for scaling are plate heat exchangers, those you might find in a high flow combi or on a thermal store .................

 

[D_Hailsham]

I would like around 20 litres a minute from the shower. I want that in all weathers, so let's assume the incoming temperature is 0 celsius and the showerhead temp is 40 celsius.

The power required to raise 20 litres a minute by 40 celsius is 56kW.

A more appropriate incoming water temperature would be 15°C. This would require a 35kW boiler.

 

[Donkmeister]

A more appropriate incoming water temperature would be 15°C. This would require a 35kW boiler.

Even in winter? The water coming out of my kitchen tap is nowhere near 15 degrees at the moment, perhaps your local bedrock is warmer than mine!

I recall an article about ground-source heat pumps that mentioned a figure of 4 celsius for the ground temperature, so assuming that as an incoming temperature that would still be 50KW.