Combi boiler - long wait to get hot water

[ChrisJ]

We had our old boiler exchanged for a combi and its great having hot water whenever you want it and our gas bills have reduced. However the problem I find is that if I just want to wash my hands or rinse a cup out I have to run the water for about 30 seconds to a minute before warm water comes through. I'm not sure how our washing machine copes. Is it just our boiler? None of the pipe runs are particularly long. Once the hot water is through its great.

Anyway..

We are about to move to a house where they have a normal boiler that we would like to replace so that we can remove the header tank in order to enable us to convert the loft more easily, free up space in a cupboard where the hot water storage tank is and so we can have instant hot water again. However it would be nice to have 'instant' hot water rather than having to run so much cold water away. Is there a way to do this? Is it possible to fit a small hot water storage tank that would suffice for hand washing/ rinsing cups etc that is topped up by the combi?

ChrisJ

[IMM]

ChrisJ,

Most modern combi's have a small cylinder inside to overcome this lag problem, or some have pre-warmed heat exchangers. Try a condensing combi to keep bills right down. Worcester-Bosch do the Greenstar, a 40kW version, delivering instant hot water at 16 litres a minute. A few others are around with similar flowrates.

[Andy Hall]

A small electric undersink heater with storage could be a good solution for that.

.andy

To email, substitute .nospam with .gl

[chris French]

In message , ChrisJ writes

You can get combi's with built in storage tanks.

[IMM]

As Chris wants a new combi, purchasing a combi with an integral storage vessel is the answer, especially when heated by gas a 1/4 of the price.

[Toby]

As stated about the Worcester Greenstar Condensing Combi - "Key features of the Greenstar include the pre-heated domestic hot water heat exchanger. After the store has reached temperature hot water is delivered instantly to the outlet being operated. The temperature and frequency of the recharge of the store may be pre-set. Modulating central heating and domestic hot water outputs, combined with separate consumer controls, also mean that comfortable temperature levels for both can be set independently of each other."

[ChrisJ]

Does that meant that for short runs the boiler won't fire up but will use water in the small tank and if you run the tap for longer then the bolier kicks in?

EG I rinse a mug out, 5-10 seconds of water, boiler doesn't fire up HW comes from mini storage tank. I wash my hands water comes from hot water store until its level drops to a certain level then boiler kicks in and supplies water to tap and refils storage tank I have a shower water comes from hot water store until its level drops to a certain level then boiler kicks in and supplies water to shower and refills storage tank when I've finished my shower.

I don't want to be heating a whole load of water I'll not be using or I'll be in the same state as the house is now with a boiler and a hot water tank.

Any one suggest a website where I can find out more?

Chris J

[IMM]

The tanks are usually well insulated and small. Some combi's have stay warm heat exchangers. The boiler keeps the domestic hot water heat exchanger to certain temp, so when hot water is drawn off there is no lag. The Greenstar has a pre-heated domestic hot water heat exchanger. This is usually user switchable, so you don't keep the heat exchanger hot when away for 6 weeks.

The lag is mainly because of the priming affect of the boilers fanned controls. On start up, it has to purge the burner box with fresh air by running the fan and determine if the fan is running, then the gas valve switches in. This takes a little time.

The crappy Ravenheat condensing combi reduces the lag time by having the fan continually run, so the gas valve switches in as soon as there is flow. This costs more in electricity to needlessly run the fan and it also extracts heat from the heat exchanger dumping it to the outside air. In sub-zero temperatures freezing air is being drawing in so the frost controls cut in to protect the heat exchanger and fire the burner, again wasting fuel. Best avoided.

[John]

In some of the older combis there was a switchable preheat facility which allowed the user to control keping a small store of water hot for immediate hot flow on demand. More modern simple ones have largely lost this facility in the name of progress and the drift towards plate type heat exchangers rather than small calorifiers within the casing of the boiler. You could select a current combi which does keep a store of hot water or stick with a storage system. Can you find room for your extension by perhaps relocating the tank and cylinder or changing to an unvented cylinder whcih would at least "lose" the storage tank. With a cylinder of either type you can have an immersion heater as backup in the event of boiler breakdown.

The delay is due to the physical limitations of the boiler going through its ignition and proving sequence before actually lighting the fire so to speak. One of my customers was extremely pissed off when he moved away into a new house with a Sime "ordinary" combi which took about 40 seconds to deliver hot water each time from cold and his water bills suddenly were higher than his gas bills

[IMM]

..and efficiency.

Plate heat exchangers are smaller and far more efficient.

He wants a combi after having one previously. He sees the great benfits.

Bad expensive move. He wants a combi after having one previously.

...and is expensive to buy, large, and requires a BBA plumber to install. Bad idea. A heat bank is far better, probably out of your experienece, but you should get to know.

You can have a small instant electric water heater on the outlet of the combi for backup, installed under a sink, at the back of a cupboard, etc. takes no space.

That is a point in any water system with long dead leg hot water pipes too. This lag is not just applicable to combi's.

[Andy Hall]

Yesterday, when I suggested that idea, you poo-pooed it.

Has the wind changed?

.andy

To email, substitute .nospam with .gl

[IMM]

You suggested a "storage electric heater" in place of a no lag combi (no internal storage vessel or keep warm exchanger). Which is very different. Having a storage heater in-line and using it to reduce the lag to the taps, will not entail using a hell of lot of electricity as the water in the electric storage vessel would be replaced by hot water from the combi. It will use electricity to re-heat as it cools.

Best have an "instant" electric heater on the combi outlet as a backup, then it will do a shower (well at least get you wet and washed).

[Andy Hall]

No I didn't. I simply suggested the electric heater as a solution to be fitted near the point of delivery - I didn't mention the combi at all. Even with water stored in a combi, there is still the cool water in the pipes between it and the point of use.

That could be done, and I didn't exclude it in what I said. However, the electric heater would be filled with cool water from the pipes even in this case, so I don't think that it is that big a win.

I'm glad you qualified that.

All of this does strike me as additional reasons as to why combi boilers are rather limited in function and performance.

.andy

To email, substitute .nospam with .gl

[IMM]

The thread/point was about combi hot water delivery lag.

That is the case for any water system, cylinder or not. A combi is generally located in the kirchen near the most used tap, so less dead leg draw-off.

That "is" what you said.

An "instant" in-line electric heater is for backup in case the combi is down.

You really haven't a clue have you? A reduced lag combi will perform just like a cylinder system in speed of hot water delivery and even better if the combi is in the kitchen. The instant in-line electric heater is for backup only. Got it? I doubt it!

And England have just taken the lead against the Aussies 17-14.

[IMM]

And England have just won the world cup 20-17. :) :) :)

[Andy Hall]

.. and I suggested a reasonable solution for it.

I know what I said, and it was quite clear.

Pretty useless, even if a moderately powerful one requiring heavy grade wiring were used. A poor backup compared even with a cylinder plus immersion heater.

I didn't say that it wouldn't

A rather silly suggestion.

In fact England won. Try and keep up.....

.andy

To email, substitute .nospam with .gl

[IMM]

A silly one when combi's are available that eliminate this problem. the OP was after a "new" combi, not attempting to rectify a problem on an existing unit.

Some electric instants can manage two taps. It is for backup for a day or so when the combi is down. Not everyone can have an unnecessary large cylinder.

What suggestion might that be?

I wrote that when they had "just taken the lead against the Aussies 17-14". Duh!

[Andy Hall]

Doing what? Certainly not delivering any meaningful supply. You'll be saying that electric showers are worthwhile next.

There are loads of benefits in having a store of energy in a cylinder either directly or as a heatbank (as you often say yourself).

Exactly. Situations change rapidly, just like your suggestions......... :-)

.andy

To email, substitute .nospam with .gl

[IMM]

You really are not that bright are you? the electric instant is for a bnackup only. You will have enough hot water to fill a sink or two and have a low grade shower. The washing machine and dishwashers will have their own electric heaters. The point you will have hot water. Got it? I doubt it.

You didn't read did you, or not bright enough to get a simple point. The man wants a combi for the clear advantages it gives, which is not having a cylinder taking up space and not to mention the installation costs of one.

England hadn't won when I hit the send key. Duh! Did you want me to predict the final score and who won at the time?

[Hellraiser]

FFS children, either answer the question or shut up, there is no need to argue like a pair of 5 year olds. I'd imagine the guy who asked the question has gone off to find another group already!

Hellraiser.......>