420 litres per hour, Combi possible?

[HarrowToCroydon]

Hello.

Water company just came to replace their outside stop cock as it had rusted.

Using the tap in garden just did a flow test. It took 84 seconds to fill a 10 litre can. Would equate to 420 litres per hour. Sufficient for installing a Combi?

That's really low flow you have at 7ltr per minute. Test again at all tap points to rule out a flow restriction with the point you tested. The below are maximum outputs which gives you a good indication. The boiler doesn't need maximum flow but there are specific minimums needed that vary by model.

24Kw combis give 9-10 l/min
28/30Kw combis give around 12 l/min
35/37 Kw combis give around 14/15 l/min
40-42 kW 16/17 l/min
approx 50-54 kW 25/26 l/min

Thank you @DrySherry
We have a Heat Only boiler with a hot water cylinder currently. The boiler has broken down. Not urgent to replace as we are away for extended periods of time.

I got my friend to re-do the test. What we noticed that with the Kitchen Sink Tap open and our Upstairs Bathroom Tap open, the flow in the garden tap remained at 420 litres per hour.

I may add that when I shut the mains stop cock inside the house, the Garden Tap, Kitchen Sink Tap and Upstairs Bathroom Tap run out of water in under 30 seconds.

I mention this, to possibly indicate that the 3 taps are mains fed and NOT fed from the overhead tank. IF THIS IS THE case, then should the mains flow be a minimum of the flow rates of Garden Tap + Kitchen Tap + Bathroom Tap?

@PigletJohn?

No.

But test the kitchen tap as well.

Fill a bucket and time it.

For example, how many seconds to fill a ten litre bucket.

Calculate lpm.

How old is your house?

Look at the supply pipe at your internal and external stopcocks. Is it iron, lead or copper, black plastic or blue plastic? Is it the diameter of a banana or a finger?

How far is it from the road to your internal stopcock? Is there garden, gravel or concrete between?

Thank you @PigletJohn I will come back to you once I can ask my friends to help. Being Christmas, it may take a week.

Have a Happy Christmas.

@PigletJohn

Some questions I can answer immediately -

How old is your house?
1952 built.

How far is it from the road to your internal stopcock? Is there garden, gravel or concrete between?
Between the road where the main line runs to the internal external stopcock is around 4 meters. And the run between external stopcock to our internal stopcock is around 10 meters maximum.

The external stopcock is in our front garden. Then I believe that it enters the house and a pipe runs below the floorboards to our kitchen where the internal stopcock is.

As I mentioned in the earlier post, our stopcock outside was "rusted", Affinity Water came a few days back to change it. (All of this I am managing which not at the place myself).

It's rather curious that a stopcock should be "rusted" since they are made of brass.

Did they fit a meter?

From what you describe it would not be very arduous to dig a trench and run a new, larger, plastic pipe under the floor. Unless you are at the top of a hill or in an isolated rural position it would be pretty sure to greatly improve your flow so you could have a combi, if you thought it appropriate, or an unvented cylinder which is much better.

Re"rusted" - When I could not locate the outside stop cock, whilst all other properties had their stop cocks on the footpath, I decided to call Affinity Water. Their engineers came and with old records found that the stopcock was inside our garden. Upon inspection they said the stop cock best be left untouched as it may break/get damaged if they touched it, they surmised it may be from when the house was built. They then returned to change it. I had requested Affinity Water to put in a meter too, they said they can do it, just a different team.

I am waiting for my friend to go and lift the lid and find if they have indeed fitted a meter too. I will attempt to call Affinity Water and check what their engineers recorded back.

"From what you describe it would not be very arduous to dig a trench and run a new, larger, plastic pipe under the floor. Unless you are at the top of a hill or in an isolated rural position it would be pretty sure to greatly improve your flow so you could have a combi, if you thought it appropriate, or an unvented cylinder which is much better."

You are quite right, between the external stop cock and the wall of our house there is maybe 2 meters, maximum 3 meters.

I would need to lift the floor board in the room where I suspect the pipe enters the house. The house has a concrete bottom then an air gap of about 2feet and then out floorboards start. Would you suspect that the cold water enters the house immediately where the room closest to the outside stop cock is? And that it then runs across the house, just under the floorboards to the kitchen?

I am HAPPY to dig the trench with a friend, but are they any pit falls I need watch out for? I have looked at online and on various water company web sites where they have documentation about changing pipes between the water company stop cock and our internal line. But is there a "catch" or "pitfalls" I need watch out for?"

" or an unvented cylinder which is much better.", there is a debate. Combi or Unvented? Our house is tiny (it's in Harrow), it has a foot print of 40 sq. meters (with upstairs 25 sq. meters). Currently a dead boiler (heat only) in kitchen, with vented hot water cylinder (with backup electric immersion) on first floor landing and 2 tanks in loft. I put in a Salamander dual pressure pump for our showers, and this works very well. I SUSPECT the cold water for our showers comes from loft tank.

Unvented, under pressure cylinder would give me hot water pressure, but what about cold water pressure? Will I still need the loft tank to supply showers?

CONFUSION REIGNS - PLEASE HELP

Ideally - I would like to replace my heat only boiler for another heat only boiler as this is the quickest and easiest option. But plumbers (2 of them) have said that best I replace the vented copper cylinder tank too as it will have an awful amount of limescale.

One plumber said that I should go for an unvented, under pressure hot water cylinder.

Another said that I should go for Combi (Vailant specifically as they come with 10 years parts+labour warranty).

The Combi will allow us to remove the current vented cylinder and tanks from loft, and space is at a super premium for us.

With our confusion what do you suggest? I am happy to carefully consider options. I am not in a hurry either.

Some points I have forgotten to add -

We have a bathroom on the first floor with a shower and toilet, it is this bathroom that all 4 of us use.

We have a 2nd bathroom downstairs with a shower and toilet but only the toilet is ever used.

1. The old water pipe may be buried until it rises it through the kitchen floor. In some cases it is visible under the floorboards. I think you will run the new one under the floorboards. Lag it with the thick "byelaws regulation" foam sleeve. In damp conditions and where buried you can get a black, synthetic rubber lagging which is more expensive, but you will not need much. Armaflex is a good brand. You can slide it over the plastic pipe as you work, so it does not need to be slit. Joints must be taped, they sell a special matching tape. Your plumbers merchant will have it.

• The new pipe does not have to follow the same route as the old.
• Trench minimum depth is 750 mm.
• Maximum depth is 1350 mm.

The water company will want to inspect before you fill the trench in, unless you use one of their qualified contractors at great expense. They probably have a leaflet or Web page with the requirements. If you have any lead pipes ask them to test your drinking water for lead content IMMEDIATELY. It must be done before you start work. There might be a lead removal subsidy, or free reconnection.

I would go for 25mm blue plastic pipe. 32mm is better if you have a larger house with two bathrooms.

Be sure to use full-bore stopcocks and connectors. They are more expensive but it is a hundred times easier and cheaper to fit them while installing than to dig it up later. Provide good access traps and do not pave or plant over them.

You can add garden taps at the same time

You can supply your cold taps and your hot water system at the same pressure. I recommend copper 22mm pipes to at least your bath and hot water system. You will not need a cold water tank for the taps, but there may be a small one for the boiler.

This is a good time to consider a water softener, or at least providing the connections for one, if you are in a hard water area. I recommend 22mm/ 3/4", not the more common 15mm/ 1/2" valves and pipes

The high pressure may make old taps and showers leak, so budget for new. I do not recommend ceramic taps. Aquilisa round bodied shower mixers are IMO the best. You can get modern silent valves for WC cisterns, I use the Opella or Torbeck but they are prone to grit blockages after doing plumbing work. When you know how it is easy to rinse out.

Plumbers are weedy little fellows with petal soft hands so the trenching is usually done by a builders labourer, a groundworks company, or a lady gardener capable of growing potatoes

1. I recommend an unvented cylinder.

Get one bigger than you think you need. It can go anywhere in the house (but please not the loft). They have amazing insulation. A bath uses about 100 litres so people often fit one about 200 litres so you can have two baths in quick succession, and only need to run the boiler about once a day.

You can have an immersion heater at the top and bottom so you will still have hot water on the rare occasions when the boiler is out of action.

Opinions differ, but I am very happy with a heat only boiler. They have less in them to go wrong (some much less).

Unvented cylinders are great if you need a lot of hot water at high pressure quicky. So running two showers at once.

As pp says the insulation on them is great and the stored hot water lasts a long time. It doesn't really matter in winter anyway as with the heat loss they just act as an additional radiator.

The immersion heater you get with them means you have a chance to heat water up even if the boiler is offline/breaks down.

The downside is the cylinder takes up space and obviously is more expensive than a comi boiler alone. If you don't have high pressure pipework you may find that if you install a unvented cylinder your pipes will start knocking with the higher hot water pressure.

It sounds like you do not need the unvented cylinder, but you might want to think ahead. Is there any scenarios where you might start using two showers at once (kids growing up), or are you thinking of selling the house at some near point in the future ? Then the unvented cylinder is a sales point.

If you feel you will never want two hot showers at once and don't need the electric backup then maybe a combi is a cheaper and viable option, especially since you need the space. I have a new valiant system boiler with an unvented cylinder, it is really small and neat - I am pretty sure you will find a really nice compact unit if you want one.

@PigletJohn . Why do you not recommend placing a pressurised water tank in the loft? Curious as we have thought about it.

You won't see or hear any problems until they get quite bad.

Somebody will have to get up there to service it.

Most lofts are not fully boarded, do not have good ladder access or good lighting. In summer they are unbearably hot and in winter bitterly cold. Frozen and burst pipes are not unusual in lofts, for example if the house is empty or the boiler has stopped working.