Replacing hot water cylinder

[housebrokenagain]

Long post here – sorry – first time on here My house is always finding new ways of breaking itself (circa 1900 terrace – not a lot done since then I think….lmao) It has a central heating system in it which I suspect is about 30 years old, supplemented by a boiler which was replaced about seventeen years ago. It is an Ideal Classic – vented indirect system with hot water cylinder, radiators upstairs and downstairs, cold water tank in roof, along with the expansion tank.
Now, from what I have read on this amazing site, I can only deduce that the coil in my hot water cylinder has a leak….. Expansion tank overflowing out of pipe which comes out of roof wall and drips onto footpath now constantly dripping and council now been complained to – its been going about three years apparently, one under my ownership…. I have tried various tests to ensure it is this
– ballcock into expansion tank is working just fine 1
– tied up ball cock, removed about seven litres of water (to about a third full from 5/6th where it usually sits overflowing) turned central heating/hot water on at 5pm and water comes through expansion pipe at a rate I would describe as a slow tap (ie trickling). The tank filled to halfway by 10.30pm when the boiler went off for the night. I made sure it didn’t come back on by turning it off at the timer, and by the next morning the expansion tank was overflowing again, and hasn’t stopped since. 2
I surmised this means that water is coming into the central heating system somewhere which has led me to the coil in the cylinder – if this has a crack/hole in it then the pressure from the cold water tank in the roof coming into the tank will push more water than necessary into the central heating system via the hole in the coil, and therefore into the expansion tank. 3
I hope you’re with me so far and this is making sense – I’ve numbered it all so you can reply and say I’m wrong about any particular bit.
So, I need to change the hot water cylinder right? 4
Now, I get how you drain cold water tank in roof (no gate valves or anything so luxurious on this system….) – turn off mains water supply, turn on taps, empty tank no pressure from above. 5
This is where I get a little hazy – if I empty hot water cylinder, will water from the central heating system not then fill/not allow me to empty to cylinder as it comes through the cracked coil? If this is the case I presumably need to drain the central heating system via the radiator with a drain-cock on it downstairs. If I turn the radiators off at both ends this will save having to refill them – question is though – how do I know I have reached a level in the system which would ensure the coil is totally empty so it does cover my bedroom with horrible dirty water when I take the inlet/outlet pipes off? Presumably wait until the expansion tank is totally empty, and then go quite a lot further? 6
Or could the central heating be on a separate loop to the coil and thus just require this loop draining? 7
From here, I have to drain the tank itself – some numpty has put in the cylinder so close to the skirting board that you could not hope to get a hose over the end of the drain cock– its almost like over the years the drain cock has settled into the skirting board. Do copper pipes have enough bend in them to risk moving the tank across 10mm 8 to get a hose pipe onto this drain cock or do I have to siphon it out of the top hole (hot water out) 9 and how do I ensure this hot water out pipe is totally empty 10 (same dirty water/carpet issues)
Now, assuming I can get this tank out, the real questions begin –
Are tanks made to standard specifications (ie will the holes be the same distance apart on a new equivalent sized tank) or is there a chance I will have to modify pipework? 11 As I have no experience of this. Cylinder is covered in yellow insulation – think I read somewhere this would tell you roughly how old it was (?) It is the type of foam that came already attached with the cylinder from new and is more like smooth finished dense polystyrene, not roof lagging stuff. 12
Now assuming I have this new cylinder sitting there plumbed in, all tightened with PFTE tape at the joints – how do I know the thing won’t leak when I fill it with water, as it wouldn’t take much to ruin the bedroom and the ceiling below – or is it fill it and keep your fingers crossed? 13
And any tips for refilling to avoid airlocks? Both cold water system and central heating system.
Am guessing (again!) that with the cold water system – as per reading on different threads on here and putting them together – open all cold and hot water taps and then turn mains back on. Hope for best. 14
On hot water system, allow expansion tank to refill after finished refilling mains system and cold water storage tank. This will presumably create some airlocks in the system which you would then effectively let into the closed radiators and bleed out in the normal way you would bleed a radiator. 15
I really do appreciate your time and knowledge in this – I would normally get a plumber in to help with something I was not sure of, but unfortunately I have just been laid off and do not have the money…. Great Xmas present – thanks work!! So I have plenty of time to devote to this (and finding new employment!) but not a great level of knowledge – time to improve the knowledge bit I think – thanks in advance!!

 

[EliteHeat]

Sorry but I found that incredibly hard to read, but from what I understood:-

(1) Drain the cold cistern, drain the HWC, drain the heating. Do not try and 'save' any water in the rads - this is an ideal opportunity to clean the system. Be aware that yo may need to manually operate your motorised valve to both drain and re-fill.

(2) You will be very lucky to get away with not having to modify any of the pipe-work.

(3) Use plenty of jointing compount and / or PTFE on the male tappings. There is no way that I know of to check the connections before filling. Ensure you fit a new drain-off and be ready to use it in a hurry.

If you buy a Gledhill cylinder you will find the process a great deal easier as they only use 22 or 28mm compression fittings - I will always fit these now instead of the more 'traditional' open vented cylinder.

(4) Airlocks are usually easy to get rid of. Don't worry about it until it happens.

(5) Don't be tempted to reuse your old immersion heater. Even worse, don't b tempted to fit a blanking plate rather than a new heater.

(6) Cleanse the system after reinstating with reputable products like Sentinel X800 or X400 and later protect with X100.

Finally, when it all works, bask with the satisfied air or someone who has probably saved about £400 on labour charges and knows that no one has peed in the cold water cistern or rifled through your wifes knicker drawer.

 

[swbjackson]

I'll ignore your numbering as your post is making my eyes go funny. In future try and break the post up into discreet paragraphs and then number it if necessary, it makes it a lot easier to read and understand.

It sounds as though the coil has failed in the cylinder so will need changing.

Unless there are isolating valves to the coil you will need to drain down the central heating and shut off the cold feed to the hot water cylinder. There should be a gate valve or similar on the cold feed down. If this doesn't shut off properly then you need to drain the cold water cistern off plug the outlet and fit a new valve. I always fit lever valves instead of gate valves as they are easier to operate and less prone to seizing.

While the heating is draining down (after turning it off obviously) you can set about draining down the cylinder. Firstly open a hot tap and ensure that the hot water stops running, it won't be instant. Once the hot water has stopped you can drain the cylinder. It's unusual to get a drain off that works on a cylinder so I normally syphon anyway. Chuck a load of old towels around the cylinder and knock a hole in the top. Insert a length of 15mm pipe with an elbow on the bottom into the hole and attach your hose to this. Take the hose to a suitable lower point and start the syphon going. I normally suck on the hoise but you may want to use a wet/dry vac.

Once it's empty you van take it out. I always cut the cold feed a couple of foot up from the bottom of the cylinder to prevent spillage. Also plug the primary connections with kitchen roll to prevent any black sludge spilling out as you take it outside.

It's now time to fit the new cylinder, the existing pipework may line up but not always so you may have to alter some. Cylinders come in different grades depending on the head of water above them so get the right grade.

Grade 3 10m, Grade 2 15m, Grade 1 25m

Some things to bear in mind are

1. Don't try and re-use the old immersion heater, they are an absolute pain to get out and it's doubtful the old immersion will have a stat fitted with a safety cut out so it won't comply with modern regulations.

2. The open vent from the top of the cylinder should rise continuously up and over the storage cistern. I have seen plenty of replacement cylinders fitted where the vent has been run back down to connect onto the existing tee. This can led to airlocks and is potentially dangerous. It should also be a minimum of 22mm all the way to the cistern.

3. When making the joints into the cylinder I always use a bit of sealant as well as ptfe. Just gives a better chance of a seal first time.

4. Make sure that any fittings used in the female threads are parallel and not tapered. Some merchants don't know the difference but a taper thread may not seal correctly and has the potential of splitting the cylinder.

5. I always use straight fittings into a cylinder as it's easier to get a seal than if you use a bent one. You can always come out of it with a street elbow if you need the bend tight to the cylinder.

6. When you refill the heating side don't forget to add inhibitor again but if you've soldered any joints you'll need to flush any residues away before finally adding an inhibitor. It's a good time to asses the quality of the water in the heating system and possibly add a cleaner and flush the system

7. When you fill the hot water side leave hot outlets open until you get a good flow of water from them to try and prevent air locking.

If you're not sure of your soldering techniques you can use mechanical joints but this ends up more expensive and doesn't look as tidy.

If you're unsure of your joints you can get an air test kit and air test through the open vent but do not overpressurise the cylinder.

http://www.screwfix.com/prods/72940...Test-Equipment/Monument-Dry-Pressure-Test-Kit

Hope this helps.

Damn, beaten to it, must type faster

Mike

 

[EliteHeat]

Yeah, but you added some bits I missed (lever valves etc)

 

[mogget]

When I changed my cylinder I found there was no gate valve or drain cock fitted. Once the cold water cistern was drained I cut the cold feed pipe to the cylinder (above the level of the cylinder outlet) and soldered a stub of 15mm pipe to it using a reducing coupler. To this I attached a hose which I used to syphon the contents into the bath.

If fresh water has been getting into your heating system for some time it's very likely that there will be corrosion and debris inside - you can clean the system with Sentinel X400 or Fernox F3, etc. before adding inhibitor such as X100. Don't be tempted to skimp on the chemicals as this could almost be the definition of the saying, 'false economy'.

 

[housebrokenagain]

Thankyou for you hints and tips - I shall attempt this in the next few days. Is there a time when any of you will usually be sitting near a computer in case this all goes wrong? Hahaha.
Is modifying pipework fairly easy?
The extent of my plumbing skill is having changed a couple of radiators - like for like no pipework adjustment.... I will look on here for details of how to install lever valves.
Thanks again.

 

[housebrokenagain]

Ah, also, how do I manually operate my motorised valve? Sorry, learning fast - I hope. And why do not use blanking plate? The immersion which is in there has never been connected/working (for a long time by the looks of things) Is this purely if you have no gas you have alternative? As could add this later if it became issue - at the mo money is issue, not time
Thanks.

 

[mogget]

Is modifying pipework fairly easy? The extent of my plumbing skill is having changed a couple of radiators - like for like no pipework adjustment.... I will look on here for details of how to install lever valves.
Thanks again.

I would suggest you buy a propane blowlamp, flux, solder, wire wool and a heat resistant mat. Then read up on soldering end-feed fittings and have a practice session. It's much better to learn first before you tackle the job itself, and it's not as difficult as most people imagine - as long as both the pipe and fitting are perfectly clean, and have absolutely no water in them.

Also, buy at the very least a mini tube cutter (the type with a cutting wheel that roll around the pipe), or if you can afford it 15 & 22mm pipeslices (look on google).

And why do not use blanking plate?

Because it's unlikely it will be easy to undo when you come to add the heater, and you might split the tank trying.

I should say that I am an experienced DIYer rather than a professional, and do usually check my PC several times in the day.

 

[ajstoneservices]

If you buy a Gledhill cylinder you will find the process a great deal easier as they only use 22 or 28mm compression fittings - I will always fit these now instead of the more 'traditional' open vented cylinder.

Ours have compression fittings too as standard, are less expensive and better too IMHO of course. They can be made to match the existing fittings.