Hot water not hot!

[GrumpyCrossPatch]

Following the general theme of heating related drama in this forum at the moment!

We have excellent water flow through the cold tap. However, our condenser boiler (a gloworm 30ci, fully serviced, always tests fine) seems to struggle with adequately heating that flow. If I turn the flow down the water gets very hot but it takes forever to fill the bath.

The reason for my concern is that the bathroom is being replaced as we speak and I thought new pipes and taps might help. However, the problem continues (possibly worse...) and the new shower that runs off the hot water (replacing an electric shower) is going in next week. Am a little afraid that the shower will be too cold to use. Help!

We had this problem recently, the divertor valve in the boiler needed replacing. The boiler man said one sign is the radiators nearest to the boiler warming up when they shouldn't, when running the nearby taps.

yes, it's possible that some heat is still going to the rads.

however, you always get this with a combi to some extent. Combis are rated to deliver X litres per minute of hot water, raised by 35 degrees C from the incoming mains temperature. So lets suppose for an illustriation, that the Summer water main is at 15C and the Winter water main is at 5C (I have no idea what yours is, but good insulation under the floor will help)

In summer, the boiler will deliver hot water at (15+35=) 50C which is adequate for a bath. In winter it will deliver at (5+35=) 40C which is rather cool. Put a thermometer under your cold tap to see how cold it is.

By turning down the flow rate (tap) it delivers the same amount of heat into less water, so making it hotter. The hot water pipes also need to be well insulated otherwise they will lose heat.

30kW is fairly big and should be able to deliver about 12 litres per minute at 35C rise

Fill a bucket at the hot bath tap, time it, and calculate how many minutes it delivers, tell us...

I see the gloworm 30ci has a 30kW output, at 80% efficiency ("D" rated), and was introduced about 2002. You can get 90% efficiency from modern boilers, so when the time comes, I suppose that would save you about an eighth of your gas bill.

calculate how many litres per minute it delivers

Thank you both. Some useful information to discuss with the plumber...

How old is your boiler? Admittedly the last winter we had our old combi boiler was exceptionally cold but we couldn't get the water warm enough for a bath so I was having to boil kettles and saucepans. Our engineer reckoned it was the age and that it could been limescale. As the water was colder coming into the house at that time of year, the system couldn't cope with warming it for sufficiently. Anyway, had to have a new one last year for different reasons and the problem is solved.

newer boilers tend to be more powerful. Combis are usually in the 30kW to 35kW range now, some of the older ones were less powerful.

The design now enables them to modulate the flame and fan down so that they run (more economically) at low outputs when they are not needed to run at full power, and this also helps then to run in condensation mode, which again improves efficiency and economy.

The availabilty of 30kW power is ample to heat the radiators in all but unusually large homes (for which a combi would probably not be suitable anyway).

It's 10 years old and we have definitely noticed issues last winter too. I think whatever the reason on this occasion we are probably best suckin it up and getting a new boiler. After the info you all gave yesterday I did a little research and can't decide whether we should get another combi or a system boiler. We live in a fairly average 3 bed semi with one bathroom but hope to get another shower room and bedroom in the loft in a couple of years. Decisions! Cost will play a part but I have no idea how much a system boiler and tank would cost.

piglet
I had a Worcester/Bosch 24kw greenstar installed 4 years ago. My water heat is set at 55 degrees from the boiler and is non adjustable. I have tested all rads and found that the one nearest one to boiler is in the bathroom - bungalow. But noticed this year, that when heat came back on again ( I can hear it in the rad), I was in the middle of running the hot water tap in sink, it went cold soon after I heard the heat come on again. If I had been showering at the time I would have had cold water, so not good. Does that mean the diverter valve has already gone wrong?

I happen to like cylinders, but I'm just eccentric. I'm not keen on combis except in single-occupancy homes, although installers like them because they are quick and easy to fit. Don't mind me, listen to other opinions too.

I have been very impressed with Megaflos, but you usually need a new, larger, incoming water pipe to get full advantage. Some new houses are built with a 32mm plastic pipe, but it can be quite tedious digging a trench through a concreted parking patch and side path if your existing pipe is too small.

In your case, I'd suggest turning off the CH for long enough for the rads to get cold, then run a hot bath and see if the rads near the boiler warm up, indicating a leaky diverter which can easily be replaced.

digerd

if I understand correctly, it does sound as if the cold radiators were stealing heat that should have been going to the heat exchanger for your shower HW supply, so yes, it sounds like the diverter valve.

It will be much easier for an engineer to confirm this by taking the case off and feeling if pipes are hot that should be cold. You can't trust me because I'm not there looking at it. Another cause could be if someone turned on a cold tap, or flushed a loo, thus stealing water flow, and the boiler's flow switch did not detect enough hot water running to turn the HW on.

The WB Greenstar is a good boiler, look up your guarantee paperwork to check its expiry date. Some boilers have 5 years now.

grumpycrosspatch, we had a new Worcester combi boiler fitted a few months ago (replacing a 28-year-old Vaillant) & the difference, esp in hot water flow, has been amazing - the Vaillant had to be turned right down (as you say) to get hot water out, then it would slow to a trickle & start spurting, but if you turned it up it ran tepid.

The new one provides plenty of hot water turned full on, & we have to add cold before getting in. It's the \link{http://www.worcester-bosch.co.uk/homeowner/boilers/gas-boilers/greenstar-28i-junior\28i junior}. Our house is a large 3-bed terrace with an original attic, bathroom & shower room so similar in size to what yours is/will be.

I love combis. The water just goes on & on (& we sometimes have a houseful of adults who all need showers at once)

Ponders, you have given me hope! Thank you to all of you for the advice, I will have a chat with our very nice plumber tomorrow.

NotSoGrumpyCrossPatch

and the new one uses much less gas - bonus

The only way you are likely to get a good indication of what's really wrong is getting your engineer to look at it. If it's on a service contract, hopefully they will come out given that it's not providing sufficient heat.

Our old boiler (which like yours was only 10 years old) wasn't producing sufficient hot water and then the heating didn't work when we put it on last year. Had to go down the route of a new boiler as two engineers hadn't got a clue what was wrong and the manufacturers wouldn't come out and look at it. Anyway, we had a Worcester Bosch 30si which is a condensing combi fitted. It's much quieter and we can choose the temperature setting for the heating and hot water which we couldn't do before. To give you an idea of cost we had 5 quotes of £1600-2400 (asked for that many as I know many local engineers were booked up and didn't actually expect them all to turn up). We went for the highest quote as he certainly seemed to know his stuff and on talking to friends, we had five recommendations for him. He was including a power flush and devices to pick up limescale/bits in the system which the others weren't. The engineers we had out said they would install any make of boiler but they all recommended Worcester Bosch and Valliant.

Glowworm hot water issues are frequently caused by the printed circuit board not sending enough voltage to the gas valve. Imagine a cooker gas tap stuck on simmer!! They are notorious for this problem. There are multiple other potential problems including the diverter valve and also blocked plate heat exchangers. My bet is the pcb though!

Glowworm hot water issues are frequently caused by the printed circuit board not sending enough voltage to the gas valve. Imagine a cooker gas tap stuck on simmer!! They are notorious for this problem. There are multiple other potential problems including the diverter valve and also blocked plate heat exchangers. My bet is the pcb though!

Sorry for the double post

Before I got my combi- 4 years ago, my old boiler was 40 years old and never gone wrong, only had to have a new pump, which went soon after I moved in, of course, Read up on combi's and most said they were suitable for one bathroom only and can cope with only supplying one tap at a time. So as only me here, that was fine.
Did notice after flushing the toilet, the water to cold tap in washbasin went slow, but didn't bother me. The same with the taps in bath. And I'm all on the groundfloor.
New boiler must be installed by a Corgi registered person and you must get a certificate from them issued by Corgi.

Corgi replaced now by \link{http://www.gassaferegister.co.uk/\gas safe register}

(dunno why. I liked the Corgi. & it was easy to remember )