new boiler

gas4you

If you are looking for a combi, then the higher flow rate the better.

Flow rate and pressure are not related.

In a perfect world you would have around 3 Bar and 20 l/min.

You also need to measure your flow rate when another cold tap is being used.

Your bath tap may be giving you a false result, as if plumbed correctly, the cold on the bath will be fed from the tank in the loft and not the cold mains.

I would go back and check the flow rate on your kitchen cold tap.

If you have mainly showers and occasional baths then a 28/31Kw combi will be fine. If you have mainly baths and your flow rate is 16 l/min or more then go for a 35Kw or perhaps higher.

I feel the chap who has quoted has confused you. A new heat only or system boiler (my preference) can easily be used with a gravity HW system. It cannot, however, be fitted to a gravity primary hot water system. This means that the coil in the cylinder is heated by the action of gravity, hot water rises, cools, then falls back to the boiler.

As for your quote, if this includes VAT and you trust him, I would bite his hand off.

lolly1963

Hi,
Thanks again for these quick replies. When BG came the other month he just used a cup thing on my kitchen tap which gave 11lts PM.
The other heating guy tested with the pressure guage on my garden tap in the garage at 3.1 bar then tested the bath tap(think runs on mains not from my tank, but not sure) This gave 10lts PM then whilst this was running went back to the guage thing and said my bar pressure dropped only by .1 and said that was good, but then this meant nothing to me. The problem i have is, if i am only getting 10 to 11 lts pm under the system that i have, would a bigger 35kw boiler give me any benefit as they quote higher litres pm than what i am getting now. Surely i can only get out of the hw tap what is coming out of the cold now. Am i best sticking to a heat only boiler considering that my bath and kitchen are next door to each other on the other side of the bungalow, so would make the combi boiler apx 28 ft from the bathroom and around 35 ft to the kitchen tap. I am more confused than ever at what to do!!Oh, and other half and son like to have lots of baths due to the fact that we only have a bath/shower mixer tap without a screen due to the windo overhang. Myself i prefer to sit in the bath with the shower head!!! heheheee..and i am sure they fill the bath to the max..
Many Thanks again.

lolly1963

Hi gas4you,
Forgot to mention that i actually jumped in on this thread by mistake, so the quotes mentioned on here dont actually relate to me..
Yes, i do have a gravity HW system at the moment with a pump above in the airing cupboard and a 3 port diverter valve and tanks in the loft with the header tank for the heating. Maybe i would do better to have a system/heat only boiler and have a new tank but with an emmersion thing in it, cos i dont have one on my old tank, with a new pump and parts. Perhaps this would also put less strain on my 24year old pipes and mainly old radiators, have only replaced the kitchen rad and installed a towel rail in the bathroom in all that time, but never had any leaks yet. The thing that i am worried about is the pressure going through my aged system and ending up with more probs. I am worried about whether or not i would actually save money with a combi due to the pipe runs, but if i have heat only boiler then the HW has less far to travel to the tank......thoughts please?
Ta

gas4you

You are correct in your assumptions. As you seem fairly confident now what your flow rate is, then a 24 Kw is ok.

A 35 Kw is wasting your money.

Have you checked the basics, ie that your stop cocks are fully open etc?

Not wanting to start a debate about which make of boiler to buy, as everyone has their own opinions, but there are better ones than the baby Worcester's out there that will also give you longer warranty's.

You state you have 14 radiators, but what size is your house? 3, 4 or more bed?

The number of radiators is not very important, it's the heat output needed for your property and what the radiators can emit in total that is important.

lolly1963

Hi gas4you,
Sorry, but i am confusing this whole issue....i think some of your reply relates to loates 123 who started this thread. I am a bungalow with 7 rads..
I should have started a new thread with my own probs.without thinking to start my own thread..maybe the mods could move my ones into a new thread....
Many Thanks

gas4you

Ok, sorry for not noticing. I'm off today, with a head full of cold:o

You have a fully pumped system then.

I find that it is the chemical cleaning/flushing that may find problems with your old pipe work radiators, rather than the new pressure in them.

I would doubt very much that you will need more than a 15Kw boiler if the rads are reasonably sized.

If you have a new HW cylinder, ask for a fast recovery cylinder. These hold less water but re-heat quicker, thus giving you the same or slightly more usable hot water at the taps.

Having one of these will also improve the efficiency rating of your system and help towards making it a 'best practice' installation.

heating-eng

Sorry to disagree with you but a high recovery cylinder holds less water ??not sure you are correct on this one .at bg if we fit a high recovery cylinder we would fit the same size cylinder it just has a bigger coil inside that give faster recovery that’s all .
Testing the pressure and flow correctly the way we are told to do it at bg .we would fit a pressure gauge and turn it down to 1 bar mains pressure then we would read the flow that’s the correct way to test the flow rate. if you look on the manufactures instructions normally it will tell you the min pressure the boiler will work at, it will also tell you how many L/min is required also for it to work correctly (only needed for combi installation).
If you fit an old system onto a sealed system then you would be putting much more pressure on the system up to 3bar where as with an open system would have probably never got to one bar some this could cause problems with leaks(it doesn’t normally but it could)
As for the size of boiler the installer should do a heat loss to see what is required somebody on a forum could not possible tell you what size is required.

gas4you

Thats a bit wasteful then.

With a fast recovery cylinder for a standard 1 bath property, you would replace the standard 36 x 18 with an HE85 cylinder. 85 litres as opposed to approx 130 litres.

The larger surface area of the coil then re-heats this in around 10-15 mins, therefore ensuring one does not run out of HW.

The whole purpose of a fast recovery is to store less hot water but produce the same usable amount.

The next standard size of fast recovery is the 120 litre, which is plenty for a 2 bath property.

Although you cannot give an accurate assessment of boiler size, it is easy with experience to judge an approximate size.

heating-eng

gas4you wrote: »

Thats a bit wasteful then.

With a fast recovery cylinder for a standard 1 bath property, you would replace the standard 36 x 18 with an HE85 cylinder. 85 litres as opposed to approx 130 litres.

The larger surface area of the coil then re-heats this in around 10-15 mins, therefore ensuring one does not run out of HW.

The whole purpose of a fast recovery is to store less hot water but produce the same usable amount.

The next standard size of fast recovery is the 120 litre, which is plenty for a 2 bath property.

Although you cannot give an accurate assessment of boiler size, it is easy with experience to judge an approximate size.

that,s not how we do it at BG .what your saying is that if somebody wanted a bath they would need to have the hot water turned on so that it recovers .
we would always fit the same size cylinder but with a high recovery to reduce bills and heat up time .

lolly1963

Hi,
Thanks for the replies. I think the pump on one of our pipes in the airing cupboard is something to do with the heating, we have a pipe going up a bit with a radiator type thing on which is for air (woman speak u understand!!)
I think our hot water is totally gravity fed and not 'pumped'.
Do you think it might be better for us just to replace all the knackered parts ie:heat only boiler,tank,ballcocks,pump(grundfoss) and 3 way valve. I am not sure because of the distance that a combi would work out any cheaper on the gas savings cos of the distances. Would it work out cheaper to install and straight swap the boiler to existing pipes? Also with am immersion element for back up in case of failure (i havent got this in my present cylinder as i think the builder may have been a tight wad!)
I must admit that our present system has only ever caused concern once in 23 years, once to thermocoupling on boiler and once a dirty blockage in one of the pipes coming down to airing cupboard (probably our fault through neglect!!) and not cleaning and adding stuff when we should have.