We're having the whole lot stripped out - want one that isn't 30 years old and badly insulated for the new boiler - and the installer has suggested a mains pressure cylinder. Apart from anything else the warranty is longer!
What do the team think?
Andy
as long as you put on a water softener, mains pressure is the dogs bollocks
Until the supply goes off anyway:-)
Depends on your mains pressure and flow.
On the upside
- no loft tanks
- mains pressure hot water for showers
On the downside
- higher initial cost
- requires annual safety check
- requires tundisk and pressure relief pipework
- may also require pressure regulating valve and pressure relief valve on the cold mains inlet as well
Owain
What does the annual safety check entail?
My water supply has failed twice in the last 8 months. Corroding pipework.
On 17 Aug 2015, Fredxxx grunted:
The above two items are really just part of the installation though; ie the higher initial cost. But I suppose could cause issues depending on the location of the installation.
On the downside I'd add that you might want to consider that if you are using an existing old CH system, to bear in mind that hitherto it's been used just at low pressure; will it stand being used at mains pressure, or might there be a partially corroded weak spot in an old radiator which will blow in spectacular fashion.
But then again, on the upside, if ever a pressurised system does leak for whatever reason, there's only a finite volume of water which can be ejected, compared with an unvented system which would leak forever if allowed.
Seems to heat up HW very quickly too.
We had one of these systems installed about 12 years ago and I love it, especially for the showers (nothwithstanding the spectacular leak within the first week!)
I think mainly eyeballing to check all is working as it should - notably the safety features - and checking the status of the sacrificial anode in the tank, if it needs one.
Indeed.
I think you are conflating some issues here... the "mains pressure" bit here is the DHW in the tank and has nothing to do with the primary heating circuit that the rads are or. That could be a traditional vented arrangement if you wanted or a modern "sealed system".
The situation you describe may be valid if converting a whole CH system from vented to sealed.
If the DHW leaks, remember its connected to the mains ;-)
From:
Regular service and maintenance of unvented systems is vital and should typically be carried out annually. Maintenance tasks should include:
Cleaning and inspection of the strainer in the cold water supply to the Pressure Reduction Valve
Inspection of pressure / temperature relief valve and expansion relief valve
Manual operation of each relief valve to ensure that water flows freely to the tundish, and that they reseat correctly.
Checking of the pressure in the expansion vessel, and topping up if required
(it takes me about 10 - 15 mins to do all those on mine)
I personally like them... however, some caveats:
Make sure you have a decent mains flow rate so as to get the best from them. Basically they can deliver hot water at whatever rate your mains can supply cold. Also think twice if you are in an area that frequently gets mains water interruptions.
The conventional (old) technology is simpler and works well with minimum maintenance. The pressurised system needs regular maintenance and there are (expensive) moving parts to go wrong. Unless your mains incomer is brand new (no scale) there is no guarantees you with get more than a trickle of water to filla bath.
People will tell yoi how marvellous mainpressure hot water systems are but there are lots more parts to go wrong.
There is no need to remove everything. All you need is a new header tank (if it's a galvanised tank) If plastic it will be OK. And possibly a new cylinder.
Sounds to me that your plumber is on a work creation scheme or doesn't know anything. In other words you are being ripped off with unnecessary work and expense. ie you are being advised by a cowboy. There is never any need for a full scale rip out everything. Old copper pipe (and cylinders) are much thicker then the new and lasts virtually forever.
just shows that you dont inderstand the first thing about it.
The *central heating* is on the primary side and is not pressurised beyond what you allow it to be - usually 1 bar or so.
Only the DHW and cold water is at mains pressure.
Even that's not quite true as a PRV will be fitted, set to about 3.5 bar. There will be a safety valve after this set to open well before the safe working pressure in the cylinder is reached (probably ~7 bar). This may be combined with a temperature limit too depending on the heat sources feeding the tank. Solar and solid fuel can get bloody hot.
You generally can't use solid fuel for heating unvented cylinders...
On 18/08/2015 08:33, harry opened his mouth, primarily it seems to change feet:
It works - how well varies enormously from adequate to feeble.
Not sure what your definition of expensive moving parts are, but one might argue that a shower pump required to get a decent shower out of a conventional cylinder would count as one.
As everyone else has mentioned, a decent flow rate and pressure on the mains are prerequisites
The two statements are unconnected... The second is possibly doubtful.
A conventional system has one valve / moving part in the cold cistern, and probably a zone valve in the primary of the CH feed. So two in total.
An unvented system has a combined control valve on the inlet (over pressure, and PRV typically), and a over temp and relief valve on the side. Plus the expansion vessel. So in all five moving parts in place of two - hardly "lots"
There is also no cold cistern to overflow, freeze, acquire dead wildlife, or leak through your ceiling. No need for shower pumps.
Erm, that pretty much counts as removing everything.
Alternatively, he has seen that there is a decent flow rate available from the mains, and has recommended a system that will give far better performance to the customer.
Well when it comes to dodgy advice, you are the master.
same for usenet posters huh...
Until it doesn't - and at 30 years, it will be only a matter of time before something leaks.
Also (surprisingly) harry seems to have missed the other significant points:
The old cylinder is poorly insulated. Yes this could be improved with a jacket etc, but it will be difficult to get it to the standard of a modern cylinder.
Secondly, the old cylinder will have a very low efficiency heat exchanger. This will result is very slow recovery, and high flow return temperatures for the boiler - leading to further loss of efficiency there as well. A modern unvented cylinder will be able to take the boiler's full output during recovery.
The shower is downstairs. Upstairs we only have a (brand new!) bath and basin. The current shower works fine - in fact, it has a pump and we've turned it off as unnecessary.
The loft tanks are plastic. A bit sludgy, but plastic. They're also under thatch which should help protect from frost.
OK, thanks everyone. I've raised my concern over the downstairs bathroom radiator - it has a large blister which might be full of water. But WTH that's on a solid quarry tiled floor.
Andy
Its a bit unclear from your original post if you are also converting your CH primary side from vented to sealed (i.e. typically with a new boiler).
If so, then yes you may in theory get failures of stuff that was on its last legs anyway - but in general, problems are rare. (I have converted several vented systems to sealed operation and not had a problem so far).
My experience is that water in one room will often spread into another, and at the most inconvenient time possible.
Personally I would examine the blister a bit more and replace if necessary at the same time as your other work.
The right time to do it is when he has the system drained. If it's full of water it'll drop a teacup full on the floor, and that will be it.
Andy
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