Hot water cylinder questions and options

[Buzzark]

Hi all, visited the site a few times over the years for useful tips but now I have a query of my own.

We have a Glow Worm hideaway 70B which heats the cylinder in the loft via gravity. The central heating is operated via a single pump which a replaced the day after we moved in 9 months ago as it had burned out due to dripping pipe from the previous owners washing machine removal.
There's no wiring to a cylinder thermostat as far as I can see.

I drained down the hot and cold water to replace the service valves that feed the shower with full bore models to eak out a little more flow/pressure yesterday.

After refilling the system it took around 90 minutes to heat the water.
I have no idea if this is normal or not other than the previous system we had at the last house which took about 30 minutes to heat the same size cylinder.
The supply into the cylinder was nice and hot and coming out was cooler but still reasonably hot.

So - a few questions regarding my setup;
1. Is that sort or recharge time "normal" assuming the details are enough for a rough guess of expected performance?

2. If I pump the hot water up instead, does that improve performance?

3. I'm assuming the coil in the cylinder is probably just a small one as we aren't in a hard water area so I don't think it's scale - does that sound right? It's a grade 4 cylinder

4. I may replace either with a fast recharge cylinder, how much better are these over a normal one? are there better versions e.g. stainless / upgraded insulation available?

5. I may replace with a thermal store and get the flow I want for the shower but money as always is limited. Any suggestions on which offer good/better value?

6. Given there's no current cylinder thermostat, I'm guessing the boiler has one built in that works on the return feed?

I should probably stop typing now!
Thanks in advance.

 

[Bamber gaspipe]

1.Is everything working & you have heating/Hot water?
2.If Yes, Go away.

 

[gas4you]

I would expect a gravity cylinder to take around 60mins plus to heat fully, perhaps a bit longer if rads on.

If you add a pump to the hot water side this will speed up the reheat cylce, but watch out for the open vent/cold feed configuration you already have. You don't want to cause pump over

Fast recovery cylinders will only work on pumped systems, they have a pancake coil in the bottom of the cylinder. I always fit these on pumped systems now, a one bathroom cylinder is smaller than the old 'norm' and reheats in around 10/15 mins. The principle is it reheats very quickly as water drawn off so you store less. Draw back is if boiler breaks down, immersion will only give enough for at max 1 bath.

The only reason to fit a thermal store is that you get mains hot tap water without it coming under G3 building regs. I have one in my house, forced upon me by national builder, but would never choose one myself. Go for an unvented cylinder such as the Vaillant Unistor.

Your current means of hot temp control will be the boiler stat, so basically how eve hot the water is in the boiler for the rad circuits this will eventually be you hot water temp. Can be very dangerous due to scalding etc.

If you can afford it go for a Unistor and change your system to fully pumped and a new programmer kit etc. You will reap savings in gas fairly quickly

 

[fumb]

DIT Thermal Store
There's some good info in there from a few sources. I have ended up building mine using the components mentioned

My experience so far has been good with a but....

The Store side is excellent. I have mains pressure hot water for fairly minimal outlay. All good
The but is I still have the old boiler setup so it's far from economical (no worse than the gravity fed system mind) and mine also is very slow to recover. I work away from home Mon-Fri so switch the boiler off. In this cold snap it takes circa 3 hours to heat the cylinder with the rads bringing the house up to temp

I also had no cylinder thermostat but I have wired one in now

 

[Buzzark]

Thanks guys, some very useful insight there which clears things up - although doesn't actually make the decisions easier!

fumbduckI've read your thread, the original and the part deux version.
Very interesting and appealing from a cost point of view especially.
Your boiler is quite a bit older than this one although this one won't be up to current standards it's probably much better than the old cast iron one we had in the last house.
It sounds like if I go this route, I want a good quality fast recovery cylinder as a basis and convert to pumped DHW.
I'm guessing your cylinder isn't a fast recovery one and that's half of the downside?

gas4you
That fills in a lot of grey areas for me!

Sounds like whatever I do, I need to convert to pumped DHW.
I'm assuming I'd want to pump the return flow to the boiler giving the pump a cooler life and avoiding pumping over?
I upgraded to a Sunvic programmer when I fitted the pump as I wanted more control and this will support extra pumps and valves etc

Yes, the thermal store's main advantage for me was mains pressure (for a shower) with DIY install ability.

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So, what I ideally want to achieve is to have a fairly powerful shower with enough capacity or a speedy recharge so that my shower (I go second!) doesn't get cold before I'm finished.
Unfortunately, I'm somewhat limited for cash as having not been in the house that long, there's a long list of things still to do and having done quite a bit already we pretty much wiped out all the savings.
Options;
1. A £500 budget would be ok at this point so for that sort of money I could probably convert to pumped, fit a fast recharge cylinder and add either a shower pump or add on/convert to a thermal store to get the mains pressure shower (e.g. using the DPS Hi-Flow BZ kit)
I'm not such a big fan of shower pumps though having replaced 3 in about 7-8 years previously.
2. Fit a thermal store. Closer to £1000 I think because I can still save by doing the work myself. More of a stretch cost wise and there is some debate on why (long standing standing and heated debate often!). I do think the engineering principle behind it is sound though, I can't really see the downsides.
3. Get an unvented cylinder installed. £1500? There are obvious benefits like pressure, simplicity and flow. There are two downsides, the first being the annual inspection costs, but I don't think that bothers me too much but it's all got to be considered longer term - £50ish? The second is the cost including the install - really, it's out or range at the moment and at that sort of price wouldn't I be better off going for number 4?
4. Install a new combi - more efficient boiler plus mains pressure water, no tanks and cost similar to an unvented system. £1500-£2000 installed is the problem, that money could go elsewhere many times over.

Had a W/Bosch CD35i II in the last house for a year before we decided to move (doh!) and it halved the gas bills, gave a great shower and we always had hot water. I know 2 and 3 will potentially deliver more shower power and bath filling speed than 4...

Another war and peace effort and everythings as clear as mud again. I think it realistically just boils down to how far I'm willing to go with the budget. I do have to consider what's right long term though as I'M NEVER MOVING HOUSE AGAIN! last time left me a little traumatised!

Am I about right with my prices and comparisons?

 

[gas4you]

I personnally think you need to convert to a fully pumped system as a basic first. This would bring your system bang up to date in the 'pumped' area. Doing this would also eliminate any chance of pump over if fitted correctly and the pump would be in the flow, not the return.

If you do this yourself it would cost around £100/£150 for parts & materials. The fast recovery cylinder would add around £200/£250.

A thermal store such as a Gledhill boilermate would probably cost in the region of £1500 to purchase and you couldn't fit a shower pump or power shower to this.

I personally do not like thermal stores as I do not think they are efficient enough. They need the boiler to run at full temp to work correctly and if you later change to a condensing boiler then this will want to run at about 60C flow to get most efficiency from it, so the 2 technologies don't go together in my book

Unvented cylinder is in my opinion the best option but you say that this does not fit in with your budget at present.

A new powerful combi such as the Vaillant Ecotec Plus 837 should give powerful showers, reduce running costs and save space, but realistically
do not expect any combi to supply two hot outlest efficiently at the same time. Also a power shower or shower pump cannot be fitted to a combi.

 

[Buzzark]

Thanks for the advice gas4you

I personnally think you need to convert to a fully pumped system as a basic first. This would bring your system bang up to date in the 'pumped' area.

That sounds like the most logical first step, it's going to be a must for anything (except a combi) that follows.

Doing this would also eliminate any chance of pump over if fitted correctly and the pump would be in the flow, not the return.

I've given that some thought - I first assumed the return would be fully filled with water, but if I remember rightly it contains some air so water falls down it rather than flowing back as a solid mass - hence no good for a pump. Is that right?
The pump can be fitted in the loft before the cylinder can't it? In our last house I seem to remember there was a pump just behind the cylinder when they removed it to convert the pipework for the combi - 13 years, and I never knew it was there!


At this stage with the new house I expect we could throw £10k at it and it would disappear so while I'd like to upgrade the boiler for long term savings, short term it just doesn't fit. It's functioning fine but when does go, you're quite right a condensing boiler will replace it and that won't match up with a full thermal store setup.

So, the plan I think I'm going to go with is;
1. Convert to fully pumped
2. Get a good quality fast recharge cylinder, maybe extra insulated
3. Sort some extra power for the shower, either a pump or a High Flow BZ mains conversion kit
4. When the boiler fails, replace with a more efficient one - either a system boiler with an unvented cylinder or a combi depending on finances and what's available at the time.

++++++++++++++++++++++++++++++++++
Actually, just out of interest - have I got my pricing of an unvented installation correct assuming somewhere around £1500?

If it's nearer £1000 all in, it might be worth the stretch...

 

[gas4you]

When installing a fully pumped system it is usual to install pump and zone valve(s) in the airing cupboard. It can all go in the loft, but you ideally need a 1m head of water from your F&E tank.

A pump can go in the return and many were installed like this on old gravity systems, but on these the vent and cold feed were usually on the primary hot water circulation side so the pump could not cause 'pump over' in this case. new fully pumped systems are installed with pump in flow, then auto by-pass valve, zone valve(s) etc.

Try Plumb Centers centercyl fast recovery cylinders. I install these and have found to be very good. if you go for the 120L then this has a seperate off take for a shower built in.

I wouldn't think you are far out in costing for a 150 or 180L unvented cylinder, depending on location and access. Thease all need a 22mm cold mains supply to them and at least 3 bar pressure to enable full flow out of taps and to gain maximum value for money

 

[Buzzark]

When installing a fully pumped system it is usual to install pump and zone valve(s) in the airing cupboard. It can all go in the loft, but you ideally need a 1m head of water from your F&E tank.

Thanks for all your help gas4you/Dave.
I have just over 2m head from the F/E tank/s in the loft so that sounds fine as we don't have an airing cupboard.
I'll do some reading up on proper layout to make sure I have things right prior to install as I didn't see a need for a valve but you've mentioned one so I clearly need to do a little research!

Hmm, just thought, would the valve be to avoid heating the water if not required (through convection) and therefore wasting energy in the primary circuit?

 

[gas4you]

With a fully pumped system you can have either a 3 port zone valve or 2 2 port valves, heating & hot water.

With your house big enough for a 70,000btu boiler I would recommend either a 28mm 3 port valve or 2 x 2 port valves.

You could still use a twin pump system instead, but a zone valve system is more the norm. The valves only open when instructed to by programmer on and room stat and /or cyl stat calling for heat. Unless one of these is calling boiler cannot fire just to keep its self warm as no doubt yours does now on gravity hot water. Don't forget to insulate all pipe work off h/w cyl for at least 1m for part L regs

 

[Buzzark]

Don't forget to insulate all pipe work off h/w cyl for at least 1m for part L regs

The original plumbing has been done very neatly - if not so high tech but it's all well mounted and fully lagged at the moment so I'd keep it that way. I've read about the regulations annomalies - you need to lag even the cold feed for 1m even if it's not loft mounted right?

OK, things are getting more complicated now!
Let me break it down a bit so I understand what each bit is for.

Currently the system has gravity feed DHW and pumped central heating:
DHW - The programmer switches the boiler on for DHW according to the timer and the boiler switches itself on and off according to it's own water jacket "thermal limit/cutout" as there's no cylinder stat.
CH - The programmer also powers the pump on during the alloted time and this is toggled on and off by the room stat.
There are currently no control valves fitted.

Proposed fully pumped system:
DHW - Within the time set for hot water on the programmer, the programmer waits for a signal from the cylinder stat and powers the pump opens the valve and fires the boiler when required.
CH - Within the time set for heating, the programmer does the same but also opens a valve on the central heating circuit.

The system would work without the valves I expect but let me test my assumptions behind the reasoning behind installing valves:
A single water ciruit passes through the boiler which must be tee'd/split into a loop for the CH and a loop for the DHW?
I presume this is a simple piping thing outside of the boiler unlike a combi which has a diverter valve (like a 3 port valve) inside the case?

The reason to install valves is not because it wouldn't work otherwise, but to make it more efficient by preventing bleed through from one circuit to another by retaining heat in only the required circuit.
The closer the valve is to the split of the circuits the better as it reduces physical transfer. Having the valve in prevents the expanded hot water pushing a slow convection round the loop in the same principal the the gravity fed DHW operates on.

Assuming I've worked that out right, I may do the changes in stages - cylinder and pump first, upgrade/changes to shower second, install valves last to wring a bit more efficiency out of the system. I realise I'll have to drain and refill twice but though I'm capable of doing most things I try engineering wise, I know I probably wouldn't be quick enough to do all that in one day like a practiced heating engineer would.

Just out if interest, how much of a problem is the bleed through from one circuit to another? I've not noticed any radiators getting warm when just running with DHW - although I expect the installation of a pump may influence that aspect.

Sorry - a bit high on the word count again and getting further away from the original title!

 

[gas4you]

Generally you are correct. You may not get gravity circulation to rads if there has been a check valve inserted in the flow pipe work to upstairs rads

 

[Buzzark]

Thanks Dave/gas4you I'll do the work in parts then but I do intend to follow through and fit the valves, as I do try to be reasonably green - plus fuel costs these days aren't exactly ideal.