Hi there,first post etc etc Okay I'll give as much info as possible.... Changed to a combi boiler Worcester 24i about 6ish years ago and kept water tank just for feeding the bathroom - Bath, toilet, wash hand basin and a internally pumped Triton T80si pumped shower (which was teed from the cold water inlet to bath tap.) As the bath taps were hard to get behind to clean I decided to swap the bath round so there was more clearance behind them, plus the existing pipework came from that end. I used 22mm plastic push fittings on both hot and cold all the way as that was there originally. (Bear with me I think I know the answer to this) As a side note the hot supply (now from combi) if tap fully opened hot for a couple of seconds then lukewarm/cold onwards. Reducing the flow (as in turning tap off slightly) = hot water, but of course if the flow was not enough it would stop working all together. Trying to tell the rest of the family this is a nightmare, they just expect instant hot. So last week pumped shower pump gave up the ghost. Faced with a few options and decided to take mains feed straight to bathroom, bypassing tank in loft. So bathroom is still on 22mm, now mains fed. Whilst doing this I noted that the hot feed to bathroom is on 22mm from combi. So now everything is the bathroom is mains, had a couple of the push fittings pop off due to the higher pressure and will be replacing this today so........ I have 22mm mains cold feed (coming from the floor boards) to a 22mm equal tee, 1 to bath, 1 to shower (which is eventually reduced to 15mm and into the shower.) Then 22mm pipe into the cold water tap. On the hot to the bath is 22mm from floorboards to tap. Should I drop to 15mm flexi from the tee on the cold feed to feed the tap or keep at 22mm as the flow rate is just fine. Should I change from 22mm to 15mm for the hot feed, I take will help with the whole turning the tap down carry on. (Is the 22mm pipe causing the hot water flow rate issue) Last one !! I'm pretty sure now that the 22mm feeding the bathroom with hot water is too big and really needs reduced to 15mm. There are only certain sections I can get to - there is a 2.5 meter section in the cupboard where the hot water cylinder was, if I replaced that with 15mm would I see a big difference ? Or the fact that it goes from the cupboard to the bathroom in 22mm defeat that ? Thanks Kenny
just chop a valve into the hot flow en route to the bath and turn it down such that when the bath tap is on fully the flow rate is enough to allow the boiler to heat the water to an acceptable temperature - the pipe sizes are fine - put the valve somewhere where the family can't get to it, so all they need do is to turn the hot tap fully open those plastic fittings that popped off - did they have inserts within the pipe ?
Yes the plastic inserts were in, my fault totally. I know now that a couple of the fittings weren't at 90 or 0 degrees, putting pressure on the connections plus now mains pressure = wet floor/downstairs ceiling ! I have just bought a brass compression 22mm equal tee which will feed a 22mm (guy in plumbers merchant said keep things as is) flexi pipe to cold water tap. Great advice with the valve in the hot, cheers I'll try that. Is the problem the 22mm from boiler to bathroom or it's just the boiler just isn't capable of providing an instantaneous Niagra falls flow of 99 degree hot water ?
it'll be the boiler, you won't get much more than about 8l/m flow rate at an acceptably hot temperature for a bath from that boiler
Thanks alot. Flex pipe with compression installed now I can sleep without wet dreams (phnarr phnarr). Now to get rid of all the copper in the loft and the other mad ways the pipes have been fitted (not by me!!)
Kenny, just as Sean says - your combi boiler isn't very powerful. It is better practice to fit a boiler which is seemingly too powerful - say a 30kW or even larger. These will not be too powerful for your central heating as they modulate themselves down to supply just what's needed, but when you turn on a hot tap, you DO want all that power to supply a decent flow. The only difference the 22mm pipe makes is that there is more cold 'standing' water in these pipes, so it'll take a few seconds more for the hot water to push all that out of the way! But, it doesn't affect the actual flow rate either up or down, or the temp. Sean's idea of fitting a gate valve tweaked down is a nifty one. But, to be honest, I wouldn't bother - it will have exactly the same effect as not turning the tap on fully. Come summer time when the cotton is... er, when the weather is warmer along with the incoming cold mains temp, you might actually want that extra flow, so all you'd have to do is open up your hot tap fully. Until then, if your family members can't suss out that for a hot bath they need to keep the tap tweaked down a tad, then they deserve all the cold baths they will get...
No it's not rocket science is it ?! I'm personally not bothered about the hot water situation, perfect hot at kitchen sink (as it's only 4ft away from boiler) It's just the fact that once the hot is okay sometimes the pressure drops and the hot tap stops, so you need to open the tap again a little to get the water flowing again. Strange thing is the sink (which is next to the bath) gives perfect hot water even when the tap is on full. I noticed that the infeed (from the floor boards) to that is 15mm (instead of 22mm that goes to the bath) Last night I was under the floor (having a look at what I could get rid of after bridging the hot mains) and both the hot and cold split where the old hot water cylinder was. Both hot (from combi) and cold mains go straight up and (presumably into the bathroom) and the other two dissapear to the rear of the house. I haven't had a right good rummage underneath but surely there is not two separate hot feeds (one to bath, one to sink). There is only one mains cold to bathroom as both bath and sink stop when stop cock is closed in cupboard. We have an outside tap for garden hose but I'm sure that is off another pipe as the stop cock under the kitchen sink. So I'm just wondering where all these pipes go !!! All I need is 1 cold mains and 1 hot from combi going upstairs (discounting heating obviously) Spent all week last week sorting out my Linux based router, now a new project is a calling !!! Thanks again for all your replies, much appreciated.
Your hot at the kitchen is fine because that tap was designed for a 15mm supply from the off, and possibly mains-powered too (inside that tap is a much narrower bore). (Is that kitchen tap a ceramic quarter-turn type?) Your kitchen tap is acting like a half-on bath tap! The bath tap is 22mm full-bore which was designed for the low pressure supply from a storage tank in the loft - that low pressure delivery needs the full, unrestricted flow from the larger pipes. Now that your bathroom is all 'mains-powered', you can have it in 22mm, 15mm or whatever - it will ultimately give the same flow rate, so you can stick with 22mm. When you turn your bath tap only half on, (presuming it's a conventional 'washer' tap - ie needs lots of turns to turn it on?), what happens is that the heat from the hot water expands the workings inside and this has the undesirable side-effect of partially turning your tap off! The rubber washer inside is pushed a wee bit back into the 'closed' position. That's just a characteristic of some of these taps - now't you can do about it. Unless you replace it... If you were plumbing all this from scratch, you'd use 15mm pipe throughout, and that's what should now supply your upstairs. Bear in mind that with a combi - especially a pitiful one like yours - it'll only supply one tap[ at a time. Even turning a cold tap on will likely affect the hot flow to some degree.
Sorry just re read my post, I was saying that the hot at kitchen is fine as in does the job and I can cope with the restricting flow bath ritual and the bathroom sink hot is fine. So my bathroom sink is acting like a half on bath tap ?
the change in flow rate at your bath tap is prob down to the tap design, something expanding when it gets hot reducing the flow.
Kenny, in essence, I think it's pretty clear there's nothing wrong with your boiler or pipes. Your boiler is a lowly 24kW jobbie - that will never deliver astonishing flow rates... Baby, it's cold out there. So the water coming into your house will also be cold - your boiler will be heating that water as best it can, but if you demand maximum flow, your water is going to be not hot. Basin taps have a narrower bore than bath taps, so restrict the flow - ergo, hotter water. Really, it has to be as simple as that. Surely.
All part of the learning curve !!!! Honestly thanks for the advice / comments, I just needed clarification on a few things. Didn't realise taps had different bore sizes, thought a tap....was a tap. It's pretty simple to understand hot water flow through a boiler. Walk slowly over "hot coals" - feet get burnt. Run over "hot coals" - feet are cold (but boggin').
I'll be using the 'hot coals' analogy from now on... Actually, looked up your boiler - it's the 24i Junior? That can deliver up to 28kW to hot water, so not that bad (mine is only 30kW). Claims nearly 10lpm @ 35oC temp rise, or almost 9lpm @ 40oC temp rise. That's 2 gallons per minute, so should fill a 20 gall bath in 10 minutes. At a decent temp. So, your bath certainly shouldn't be running 'luke-warm/ cold' after a few seconds. It shouldn't be running luke-warm at all. And your boiler doesn't have a DHW output control - so that's fixed to just provide what's asked of it (the burner will modulate up and down as required.) So, why is your bath tap running cold? I dunno. But it must be down to the simply fact it's a 'larger' tap - no other reason pops into my hapless mind. (The only other possible reason is the exact opposite one - the bath pipework is so restrictive that the boiler doesn't have enough flow rate going through it to fire up the boiler. But clearly it's not that.) So, the only possible explanation I can think of (other than faulty boiler) is that you have a really good cold mains water flow and a flow 'restrictor' was not fitted in the cold inlet to the boiler. Ok, I don't know if the Bosch even has one supplied for this purpose, but my GlowWorm did. Can you try this: get a bucket or large container. Place it under your kitchen cold tap and turn it on full for, say, 20 seconds. Measure how many litres you have, and 'times' it by 3. That will give you litre-per-minute (lpm). Also try that with your bath hot tap - full on. (You can run them for just 10 seconds and times x 6 if you prefer - but time it more accurately )
I recall that the minimum incoming mains flow rate for a domestic is only about 10l/m - but there will be plenty of properties that will have at least 3x or 4x that, so it's easy to see how (on max flow) you'd see a very small temp rise - especially in this situation with a bath tap with a flow rate that is likely to be at least 15l/m extrapolate the quoted flow rate/temp rise about and it's clear that the result will be lukewarm
Right, just did the "tests" It took : Kitchen tap took 24 secs to fill a 15l bucket, by my calculations 37.5 l/m Bath hot roughly 1 minute to fill the same 15l bucket.......15l/m As far as I can see there is no restrictor on the mains infeed to the boiler, just straight in (unless it's internally) The tap expanding thing makes sense now I thought the boiler wasn't strong enough to "push" the water up at a lesser flow rate, hence the reason for opening the tap further. So basically : (These have been answered above, it helps when I write them down !!) The bathroom sink tap has a smaller bore therefore has a smaller flow rate hence why it keeps giving hot water at x amount l/m. Bath tap has a larger bore so it has to be "reduced" (by turning on slightly) to create the same flow as the bathrooom sink. In doing so the internals of the bath tap expand with the heat and act like a washer, shutting the flow off altogether. Just for my own ever expanding mind, what do I look for in a "non expanding tap" is there such a thing ? But the fitting of a valve on the hot infeed would solve that issue. Would be useful to install one anyway if I needed to do anything with the hot water, adjusting when the main water temps a bit warmer. It's ALL making sense now (might have taken a while), I've learned loads and feel better for it thanks a million for everyones input.
you can get in-line flow restrictors that fit some tap bodies - but you'll then not have the option to control the max flow rate as you would with a valve
Forums
Facebook
Twitter
You Tube
Instagram
Shop