hotwater cylinder replacement & control upgrade

[1tim23]

Now that my hot water cyclinder has corroded to the point that it leaks, I need to replace it (Cue for Rant: it was professionally replaced in 1996 - I thought these should last as long as the house! what's the matter with modern cylinders ?). It's a standard copper, indirect, vented one with 28mm pipework for the gravity-fed heating coil. The return from the heating coil has a Drayton cyltrol mechanical valve, now well seized up, as they apparently tend to do, and no longer working. So While I'm changing the cylinder I'm thinking of adding Sundial C plan controls, i.e. a cylinder thermostat and a 2-port zone valve (to replace the cyltrol) e.g Honeywell L641 and V4043H. Hopefully it's a simple job to connect these to the programmer and won't affect the rest of the heating system.

Various potential snags come to mind. I'm told that the existing compression to 1in BSP cylinder connectors are unlikely to come off intact so I should fit new. These will be parallel BSP, so will need some jointing compound. The old ones seem to use a translucent silicone product. I suspect PTFE tape won't be up to it. Any recommendations ?

When I fit a new (backup) immersion heater I'm a little nervous of using too much or too little force (I suspect the old cylinder is now leaking due to the stresses caused by fitting the i/h). Also, the immersion heater instructions say not to use any jointing compound, although plumbers always seem to use loads of putty for this job. What should I use, and how much tightening ?

When I fit the zone valve and thermostat I want to connect to the existing Potterton EP3000 controller (user guide long gone). I assume this should do the job if I can figure out the wiring. Any help available? Actually, the first problem will be getting the EP3000 off its backplate and getting at the connections - any advice ?

Reconnecting the heating coil will need some adjustment to the existing 28mm pipework, because the spacing between the connections is different on the new cylinder. Although I've done a bit of soldering of 15mm capillary joints in the past, I'm a little nervous of tackling 28mm. Should I duck out and use compression joints (apart from anything else, that would mean buying bigger wrenches) ?

 

[Agile]

It was not very professional to replace the cylinder during 1996 and not replace the gravity system with a fully pumped one. It was even more unprofessional if the Cytrol valve was not operating then!

I would generally not advise replacing the cylinder as a DIY project unless you have considerable experience of pipework but you seem helbent on doing it so the best of luck. Just do it at the beginning of the week in case you need professional help to complete it!

Tony Glazier

 

[1tim23]

Eh ? I thought this was a DIY forum

But thanks, Tony, I know this could get me into hot water (!) and I'm not over- keen to take it on. But then the last professional didn't do a fantastic job, as you pointed out, and I've been quoted over £600 to replace the cylinder (excluding the control upgrade). The cylinder itself cost £120.

I assume converting to fully pumped makes the job much more complex and costly. Maybe better wait until the boiler needs replacing (probably not long now, or am I being cynical? It's a trianco oil burner, about 1986 vintage).

 

[Nige F]

I`ll travel and lodge overnite for £480 labour to change your cyl. I`ll even give you the scrap value back No electrics. Cash.

 

[slippyr4]

I'm told that the existing compression to 1in BSP cylinder connectors are unlikely to come off intact so I should fit new.

They cost bugger all, so just buy new ones anyway.

These will be parallel BSP, so will need some jointing compound. The old ones seem to use a translucent silicone product. I suspect PTFE tape won't be up to it. Any recommendations ?

On a nice new cylinder with clean, undamaged threads, with nice new clean undamaged connectors, PTFE properly applied should easily do the job. Use 8-10 turns neatly applied, clockwise, onto the male thread. Don't overtighten, that will make it leak.

When I fit a new (backup) immersion heater I'm a little nervous of using too much or too little force (I suspect the old cylinder is now leaking due to the stresses caused by fitting the i/h). Also, the immersion heater instructions say not to use any jointing compound, although plumbers always seem to use loads of putty for this job. What should I use, and how much tightening ?

Follow the instructions! No jointing compound. There should be a fibre washer. That's all the sealing necessary. Immersion heaters don't need to be very tight at all. I'd guess tighten by hand, then another 1/3rd of a turn, maybe less.

When I fit the zone valve and thermostat I want to connect to the existing Potterton EP3000 controller (user guide long gone). I assume this should do the job if I can figure out the wiring. Any help available? Actually, the first problem will be getting the EP3000 off its backplate and getting at the connections - any advice ?

you could just get a new controls pack. Screwfix sell various brands, mostly at the 60 quid bracket, both S and Y plan, including motorised valve(s), programmer, room stat, cylinder stat.

Reconnecting the heating coil will need some adjustment to the existing 28mm pipework, because the spacing between the connections is different on the new cylinder. Although I've done a bit of soldering of 15mm capillary joints in the past, I'm a little nervous of tackling 28mm. Should I duck out and use compression joints (apart from anything else, that would mean buying bigger wrenches) ?

Have to admit, i've never soldered 28mm. But soldering 22mm is a bunch harder than 15mm. IMO end feed is easier than yorkshire for 22mm joints.

If you upgraded to a pumped system (which would be a good idea for many reasons), you'd probably not need 28mm pipework. Unless your cylinder is the size of a swimming pool.

I would generally not advise replacing the cylinder as a DIY project unless you have considerable experience of pipework

Boo Hiss! Where's the fun in that? In at the deep end is the best way to learn. And the satisfaction if you do it is great. Be positive: I just finished a complete, from scratch, CH and DHW install (everything apart from boiler & gas). Prior to that i'd only really done minor plumbing jobs - change a rad valve here; install a washing machine point there, etc.

 

[Softus]

Now that my hot water cyclinder has corroded to the point that it leaks, I need to replace it (Cue for Rant: it was professionally replaced in 1996 - I thought these should last as long as the house!

Nope - no cylinder will last as long as a house.

what's the matter with modern cylinders ?).

Nothing - you get what you pay for, but very few are guaranteed for more than a year.

It's a standard copper, indirect, vented one with 28mm pipework for the gravity-fed heating coil. The return from the heating coil has a Drayton cyltrol mechanical valve, now well seized up, as they apparently tend to do, and no longer working. So While I'm changing the cylinder I'm thinking of adding Sundial C plan controls, i.e. a cylinder thermostat and a 2-port zone valve (to replace the cyltrol) e.g Honeywell L641 and V4043H. Hopefully it's a simple job to connect these to the programmer and won't affect the rest of the heating system.

Depends on the programmer, but most will support a 'C' plan system in some manner or other.

Various potential snags come to mind. I'm told that the existing compression to 1in BSP cylinder connectors are unlikely to come off intact so I should fit new. These will be parallel BSP, so will need some jointing compound. The old ones seem to use a translucent silicone product. I suspect PTFE tape won't be up to it. Any recommendations ?

PTFE on the threads and LSX on the joint faces. I've never had a leak with this method.

When I fit a new (backup) immersion heater I'm a little nervous of using too much or too little force (I suspect the old cylinder is now leaking due to the stresses caused by fitting the i/h).

Why do you suspect too much force was used? Has the boss come adrift from the cylinder?

Also, the immersion heater instructions say not to use any jointing compound, although plumbers always seem to use loads of putty for this job. What should I use, and how much tightening ?

Don't use putty - no competent plumber would do that. Again, PTFE on the threads and LSX on the joint faces will serve you well and enable element replacement when it expires. Don't forget to use an Incaloy coated element if you're in a hard water area.

Reconnecting the heating coil will need some adjustment to the existing 28mm pipework, because the spacing between the connections is different on the new cylinder. Although I've done a bit of soldering of 15mm capillary joints in the past, I'm a little nervous of tackling 28mm. Should I duck out and use compression joints (apart from anything else, that would mean buying bigger wrenches) ?

If you're making onto old 1" pipework then you'll need adaptors and/or big wrenches and spanners, but soldering 28mm is exactly like 15mm - cleanliness is next to godliness, and don't bother trying to solder a pipe that isn't dry inside.

Assembly and solder as much as you can outside of the cupboard - the first rule of reliable jointing using any technique is to avoid struggling when you're doing it.

I have to tell you that there's a lot more to installing a cylinder than knowing how to make all the joints off. I'm not trying to put you off, but you ought to know that the choices you make in routing the pipework all affect the performance of the system, and you need to guard against air locks.

Also, don't forget to add a drain cock to the bottom of the cold feed - if you don't and if you have any leaks or problems (or even a cylinder failure - it happens), then you'll wish you had!

 

[Agile]

The last cylinder we replaced was a total of £440 in London so your £600 sounds a little high and you may get a better price.

I always teach people to just use a little silicone grease on the immersion element threads and washer.

Many of the current cylinders have a 22 mm compression fitting on the heating coils.

Tony Glazier

 

[1tim23]

PTFE on the threads and LSX on the joint faces. I've never had a leak with this method.

Thanks. Someone else also mentioned LSX, so I'll go with that as you suggest.

When I fit a new (backup) immersion heater I'm a little nervous of using too much or too little force (I suspect the old cylinder is now leaking due to the stresses caused by fitting the i/h).

Why do you suspect too much force was used? Has the boss come adrift from the cylinder?

The boss is OK but there's a dent in the cylinder just next to the boss. Looks like the boss spanner pressed against the cylinder when the heater was being tightened. In the dent, there's a pin hole. Probably not a coincidence, as I 've heard before that denting or straining the cylinder can stretch the metal and make it more vulnerable to pin-hole corrosion.

 

[Softus]

The boss is OK but there's a dent in the cylinder just next to the boss. Looks like the boss spanner pressed against the cylinder when the heater was being tightened. In the dent, there's a pin hole. Probably not a coincidence, as I 've heard before that denting or straining the cylinder can stretch the metal and make it more vulnerable to pin-hole corrosion.

Hm, good observation - as you say, probably not a coincidence. At least these days, assuming you buy a Part L compliant cylinder, it will be pre-lagged with an expanded foam coating which makes it harder to damage the thin copper walls.

If you want to stave off buying a new cylinder just yet, you could try sealing the hole....

When the cylinder is nice and hot, isolate the cold feed to the tank, open all hot taps, cut into the hot outlet from the top of the tank (don't disturb the connetion onto the tank because it might not want to undo), stick in a hose and syphon off enough water to get the level below the leak.

Then get the copper on the outside of the tank scrupulously clean (coarse wire wool and/or emery paper) and dry (and without rubbing the copper away!). Then apply some external leak sealant, pressing it into and through the pinprick hole. Leave a small but nice mound on the outside. Leave it to cure for an hour and then recouple the hot outlet and refill.

BTW, the only sealant I can recommend for this is Fernox LSX. There may be others but I don't use them.

If you don't have a working cold feed valve, then of course you'll have to shut the cold main off and drain the cold storage cistern, but this is far easier and cheaper than buying a new cylinder.

 

[ChrisR]

Why not use solder? Ordinary stuff would do but you could mend a massive hole if you wanted. "Tin" the area with normal (lead free best, but either would do) plumbers solder (electronic stuff would be even easier).
Then get some stick solder from a plumber's merchant. It's often called type D, but they'll only have one sort of stick solder I expect. Make sure the holy area ia tinned and the surface hot and wet (with solder!). Keep it that way with the torch and melt some stick solder off the end, dabbing the stick onto the tank. Much easier to do than describe. It won't run much, but heat it and it will a bit. You can spread it around a bit like it's cottage cheese. \You can leave it a couple of mm thick ot whatever you want with practice. Don't mress with it too much or it'll lose its flowing characteristics (burning the tin out I think they used to call it). If that happens add a little ordinary solder.
You won't have a "moleskin" but you can use a big pad of kitchen roll to flatten/shove it about. Remember it doesn't have to look pretty.

They used to use Tallow as a flux with this stuff but forget that, normal flux is fine.

 

[Softus]

I've never tried solder as a patch, but it sounds plausible.

As another idea, you can buy a 'liquid metal' product under the David's brand (you know the P40 and Isopon stuff) that you mix with a catalyst to make it go off. It would be much easier than soldering, and I believe just as strong - I used it once on a car petrol tank and it never came off.

The only problems I can foresee with both solder and liquid metal are:

1. it's quite rigid - if the tank expands too much with heat then it might crack away.

2. It won't stick too well on the inside surface - solder won't stick at all.

LSX has neither of these shortcomings - it sticks to anything with abandon and remains flexible (rubbery) when cured.

Over to you 1tim23. The choice, as they say, is yours.

 

[Softus]

I`ll travel and lodge overnite for £480 labour to change your cyl. I`ll even give you the scrap value back No electrics. Cash.

Hm. The cylinder job I did on Thursday only cost the customer £550 including a 2-port MZV & all other materials. And I did the electrics. I guess my customers are just lucky. Or maybe yours just aren't...

 

[PEDANTICVINDICTIVEMAN]

Cylinder swop about £800.00 for old folks to put up with their whingeing, even more if there retired estate agent/solicter/barrister.
Bollocckks to IH, use lashings of bosswhite on the threads or the bagger will pea out, remove cover of EP3000 with a hammer and chisel, they allways break,plastic craapp, brown paper and vinegar to seal 28mm pipes, worked for jack and jill.

 

[slippyr4]

fixing a hole in a cylinder that is due to corrosion is a false economy- there will be other parts of the cylinder that are paper thin; these will start to leak soon anyway.

 

[Softus]

PVM, if laughter is the best medicine I swear you're keeping me out of hospital