Boilers DHW baths and showers (dare I ask?)

[GMM]

Had a bit of a scare the other day when a boiler started making a whining sound. Enough to go through the house and wake us in the morning. I say 'a' boiler as we have two in tandem (large house, not my choice as they were already here 2 x Ideal ICOS24's - yes, I already know that Ideal are far from ideal). The advantage was that I could just turn the one making the noise off.

I thought it might be the fan but did a Google and concluded that it could be the heat exchanger and the system needs good flush so got some cleaner to see if it would work. I haven't used it as when I turned that boiler back on to have another listen, it didn't whine any more (Sod's Law). So for the moment, the diagnosis is inconclusive but I shall probably give it a run through with cleaner anyway very soon, now I've bought it.

The master plan had been to install a thermal store (we need to get some mains water up to the second floor and it's currently from a cylinder on the first floor with a header immediately above it. If Mr Rumm is reading this, it would be interesting to know how the unvented cylinder project went!). Then, when it became necessary, I would swap the boilers out for one large one.

In the face of a potential failure, the idea of having two boilers in tandem seems like a good one, since we've been quite happy with just one running for the past week (I know the weather has warmed up a lot and that's probably why, but it proves the principle).

The biggest reason for the thermal store idea was that combi's are generally rubbish for running a bath (I should duck here, knowing what that will precipitate) but it occurs to me they're fine for a shower (which is used more and likely to be the way to go on the top floor). The other reason is to relocate the water cylinder (or store) to space available on the ground floor and generate a bigger main bathroom.

So, a new master plan might be to: a) relocate the hot water cylinder to the ground floor, keeping the header tank on the first floor (probably a new tank involved here to ensure it can take the extra head) b) as and when one of the boilers gives up the ghost, replace it with a combi, piped to provide dhw to taps and showers.

Does this sound like a reasonable way forward? I could do without making too much of a job of it as I have other major work planned for the summer, assuming it comes this year.

In the current setup, the shower in the main bathroom has next to no head so is fed through a pump from the cylinder for hot and its header for cold. If I move the cylinder down a floor and keep the header where it is, is this arrangement likely to still work (until the time comes to put a combi in)? My conception of the pressures says it should be no different but perhaps someone knows otherwise.

Sorry that's a bit long but trying to give the necessary info.

[geoff]

In message , GMM writes

It could be as simple as a split washer acting like a reed. You need to home in on the noise

[GMM]

Indeed. Though, like any intermittent fault, tricky to do when it isn't happening....

[Owain]

They're (well, mine is) adequate, if you don't mind waiting a bit for the bath to fill up. I use the time for shave, teeth etc. It would be more of an issue if it were a 'family' bathroom with other people queueing and every minute counted.

Remember you can use a combi to run a HW cylinder (or thermal store), treating it as an additional radiator zone from the combi point of view, and keep the HW outlet on the combi for one bath or shower.

Owain

[Tim Watts]

On Wednesday 17 April 2013 20:25 wrote in uk.d-i-y:

Why not arrange for the thermal store to have a couple of immersion bosses - both low down. Then you have the option to charge it via electricity which could make sense with an Economy 7 tarrif - and gives you an elegant backup if the one boiler goes pop.

[John Rumm]

Well, so far so good - it meets expectations in pretty much every way.

There were two goals for the exercise... one was to sort the dismal hot water performance, and the other to attempt to improve the efficiency of the heating.

A summary of the problems with the old setup:

Hot water was a conventional gravity system. However given the house is a chalet style conversion it meant the header tank was on the first floor in a cupboard, about 5' off the floor level. That meant pressure to taps upstairs was as little as 2' of head in some cases. You also could not have an unpumped shower upstairs since the head would be above the tank level. In addition, reheat times were not fast given it was a "normal" cylinder heated indirectly from a fully pumped S Plan arrangement. Mains cold water is available at 5 bar and fire hose flow rates.

The second issue was heating... that was a problem in a few ways. Old cast iron lump boiler, no pump overrun, single rad zone in a property where the upstairs is a smaller and much better insulated area/volume than the downstairs. Also an exposed location with high variability in the rate of heat loss and hence heating requirements. Finally some areas of the downstairs never really achieved target temperature in spite of balancing the rads.

Options to fix:

To fix the heating system issues, I wanted to go S Plan+ with two heating zones, each with its own prog stat. Plus a DHW zone. Rad sizes needed adjusting downstairs to increase the output in some areas, and also to add one to the utility room that would lose the contribution of "waste" heat from the boiler itself. To gain maximum efficiency, year round comfort, and deal with the variability of the heating load, I decided that weather compensation[1] would be a sensible addition.

DHW really then came down to either a heat bank type of arrangement, or unvented cylinder. Possibly with a combi in the mix to feed the utility/kitchen that are on a longish dead leg of pipe.

Decision making process:

I rejected the traditional thermal store to do "everything" arrangement on the grounds that firstly it would need to be *massive* to have a hope of running 21 rads and coping with DHW demands of multiple baths / showers, and secondly I was not convinced that there would be much efficiency gain (if any) over a modern modulating boiler with weather compensation. So that left a heat bank for DHW only, or unvented. The commercial DHW heat banks like the Pandora looked ok in theory, but the quote I got was too much (pushing 2K for a 250L IIRC). Pricing the DIY heat bank, showed that it was in much the same ballpark as an unvented cylinder by the time you have accumulated all the bits. So in the end I opted for the unvented on the grounds that its easy to buy the whole system in one box ready to go, and it will also integrate with the boiler controls easily.

The boiler needed to be a "split temperature" capable device to allow for reheat on the cylinder, while still being able to run the rads at the weather compensated temperature demand (can be 40 degrees or less when its not too cold outside). That limited the choice a bit, and I also could not find a combi that would do that, so it meant using a system boiler.

Solution implemented:

Replace three rads downstairs with larger ones, relocate two of the liberated ones to replace smaller ones, and install the last "spare" one in the utility room. Fit TRVs on 9 rads that did not have them. Split the heating into two zones. Installed a Vaillant Eco+ 624 boiler, Unistor 210L cylinder, VRC470 weather compensator (also acts as main prog stat), their VR61/2 wiring centre (interfaces the 240V zone valves to the ebus system used by the other bits), and a VR81/2 Aux control to act as prog stat for upstairs.

Result:

Works nicely - downstairs is now a nice even temperature all round. Upstairs does not overheat. System is quiet and effective. Will need to see a years worth of bills to assess the impact on gas use though!

Hot water delivery is impressive everywhere (even the dead leg to the kitchen is less of an issue due to the rate of delivery). There are no obvious interactions caused by simultaneous demands either which is nice. I also have a large cupboard in our en-suite that will make a nice shower when I get the required shape of tuit. If I were doing it again, I might have gone for the 300L cylinder. The cylinder will swallow heat from the boiler at 22kW, so reheat is pretty close to optimal. The boiler also condenses during reheat, and adjusts its flow temperature as it goes to do as much of it at high efficiency as possible.

Remember you can also heat a cylinder (or store etc) from a combi as well. (although see my comments on conflicting requirements above)

Is there a loft available?

If not, then I would look at a solution that can use mains DHW if your mains is good enough.

Sounds doable certainly.

It should work just the same... you may want to move the pump to be closer to the cylinder though. The extra relative head at the cylinder should also reduce the possibility of cavitation or air ingress.

Sorry for the long answer ;-)

[1] My ideal weather compensator ought to include an anemometer as well here - since the cooling effect of the wind is noticeable.

[GMM]

I think I would certainly have one, even without the Economy 7, as a backup, even though that would give 3 different ways of making dhw (!)

[GMM]

(all snipped out as we're getting pretty long!)

Many thanks for such an extensive description, John.

It sounds like a very similar situation to here, except we have the added issue of an extra floor. The head in our bathroom is about similar to your original setup, ie nowhere near enough, and then there's another floor above that where I would like (eventually) to fit an en-suite. Unfortunately, there's no loft above the top floor, so no chance of getting any sort of head up there (ohh err vicar).

Also, we have very good mains pressure and flow. Next door measured 4 bar on the top floor and I had a new feed in from the main when we moved in just over a year ago.

Similarly, I have never considered using a thermal store for all of the heating as well as hot water: We have 20 rads and there will be UFH in the conservatory replacement/extension, but I was thinking it might be useful for feeding the UFH.

I think we may wind up with an unvented cylinder though, for the pragmatic reason of cost over outcome, much the same as you did. I don't have any sophisticated control on this system as yet (have been considering whether that, and zoning, might help the massive gas bills), just TRVs all round, but we're nowhere near as exposed and get some good sun on the back of the house.

And the underfloor insulation made a huge difference, together with some draughtproofing. I think it'll be a long time (and a lot of celotex) before we ever see a nice even temperature around this place though!

I do rather like the idea of a tsunami every time a hot tap is opened. If nothing else, it would make buying taps a lot easier when we refit the bathroom and kitchen (!).

One nagging question I did have in contemplating mains pressure hot water is whether I'll have to re-plumb the whole place to avoid leaks in awkward spots: Judging by the standard of most visible plumbing, I've a feeling it could be a real risk and I would feel a lot better if it was all in continuous runs of plastic where it's not accessible. I don't think that's as bad a job as it sounds since quite a bit of it needs changing anyway to move things around and to get rid of some runs of iron pipe. There might even be some lead at one point, if I'm guessing correctly.

Apart from the efficiency, is there any other issue with the 210L cylinder? It sounds like that should be enough to cope with most demands unless you have a lot of people in the house.

At present, I'm relieved that the boiler doesn't seem to be about to give up immediately and I have some more time to give this some thought, as it's a pretty serious investment, whatever the details.

Cheers!

[John Rumm]

Yup, I had a similar situation on the previous place when I did the loft conversion.

While you can get negative head shower pumps etc...

...in these circumstances it seems sensible to go for a mains fed solution.

Indeed it could. Having said that, the box of tricks that I used to interface my modern boiler to my "traditional" 2 port valves, also had the capability of controlling blending valves for UFH zones. It could support a couple of "controlled" (i.e. blended) zones if required.

The cylinder I used seemed pretty flexible in its installation and integration capabilities. It came with a new zone valve, and the temperature sensor that could feed the control system[1] as well as the normal stats and interlocks etc. So you can hook them up to pretty much anything.

[1] One of the irritations with the Vaillant documentation being that the boiler manual gives details of system wiring using one particular model of wiring centre. It gives the (quite logical) impression that the supplied temperature sensor in the cylinder is wired back to the wiring centre, and it communicates the required information to the boiler via ebus. It was a tad annoying to be at the hooking things up stage to find that the wiring centre had different ideas, and suddenly find you need yet another wire directly back to the boiler from the sensor. (and when it gets there, there is nowhere to terminate it, without first chopping off an internal connector that would have been used on the combi varient for its DHW water temp sensor, and chock block wiring it to that!)

Indeed, and to be fair I was surprised that I managed it here... this may have been by brute force (one or two of the new rads I put in a fairly hefty). Controlling the under floor ventilation levels have also helped.

Exterior wall insulation will be the next "big" job.

Yup.

Pipes generally are not usually fussed by a bit of extra pressure - it tends to be more of an issue when converting old vented heating systems to sealed systems where lockshields may weep or knackered rads pinhole etc.

Have a look at:

for chapter and verse...

But in general 210 is not a bad size, although a couple of showers in sequence can use it all unless you have some reheating.

If you want to heat just the once (say using overnight cheap lekky), or don't want the boiler diverted from the heating at anytime, you may need more. If however you are content to let the boiler heat it when required (which it needs to do exclusively on my system), then you can get away with less since it will degrade into a combi style system if required, with the boiler reheating the water on the fly as its being used.

I have set mine up to do a full heat in the morning before the heating is due to come on, then at a couple of other times during the day. If I know I am about to make massive demands on it, then I enable cylinder boost on the controller.

Yup, just the cylinder on its own is going to be pushing £800 to a grand by the time its in, if you DIY.

[GMM]

True -I've no doubt there are a number of solutions given a little thought (which I haven't quite fully put into it all yet!)

I'm guessing you found a good way to baffle your underfloor vents then. I recall a thread on that a while ago. Judging byt eh change in the weather it might be time to open them up a little soon (though it could be snowing next week for all we know!)

The more I think of it, the more exterior insulation makes sense though I suspect it's not an option I can implement much given the nature of the house (red brick semi).

Well, that's another issue for me - I'd like to convert my open system to a pressurised one but sort of dread opening the can of worms. Although my rads look generally OK, clearly those on the upper floors have never experienced significant pressure so some joints could be delicate without knowing it. Of course, rads can look OK and still be about to burst.... I suppose there must be a way to test whether the system can take a decent pressure, though to do it, I suspect it's pretty much necessary to swap over and by then the deed is done.

Well, dspite having a pretty alrge house, there are only 2 of us here most of the time, so I would guess 210L would do the job. There seems little purpose in skimping given the relatively low costs involved compared with smaller ones.

Given the location (sout-facing at the back), I'm tempted to have a go at a DIY solar DHW solution, so would get a solar cylinder then bodge on whatever I rig up to that. Again, there seems little to lose and if it doesn't work, msot of the lost cost is in my time.

Indeed. A grand or so was what I had in mind. Then the boiler started making what could be expensive noises and with that it could more than double. On teh other hand, the summer is the time to deal with these things, when you can lose the heating for a few days if necessary.

Once I have sorted the water, I'll be able to get started on the bathroom..but that's another story.....

[John Rumm]

Yup, I found working backwards from the desired result + analysing what bits actually mattered helped.

So for example some folks cite the inclusion of unvented cylinders in the G3 regs as being more onerous, however since *all* cylinders are now included in G3 it matters less. Same goes for servicing - the requirements are not that onerous.

I got some ali hit'n'miss vents that I mounted over the air bricks, and then throttled them down to more miss than hit on the windy sides...

I will open them up some soon.

Yup, much harder to preserve attractive brickwork... there are some systems that allow for brick slip panels to be fitted - but even then you would need to do something at the join to the semi to hide the thickness change (unless you can talk the neighbours into doing it at the same time)

Well I have done it a couple of times now, and so far not had a problem.

I think they need to be pretty close to failing anyway for it to matter.

I suppose you could add a filling loop and pressure gauge, and temporarily block the vent pipes to test.

Yup the price delta is not huge from the smallest ones.

The solar coil will add a little to the price of the cylinder, but as you say not much in the grand scheme, and if you can contrive some way to use it, it would probably pay for the extra cost fairly quickly.

Yup, I originally expect about 2k, but by the time you add on three new rads, several electronic boxes of tricks, blending valve, new TRVs etc, it soon creeps up. In the end it was just under 3k all in.

Glad I got mine done in the remnants of summer last year. Its certainly been more pleasant to live with... might even save some money as well with luck!

;-)

Yes I have a nice shower sized space that used to hold cisterns of various types, just waiting for some attention.