Anyone in the market for a new combi boiler and fancy a free upgrade?

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Anyone in the market for a new combi boiler and fancy a free upgrade?

29 posts & 11 voices | Started 4 months ago by andyl | Latest reply from bruneep

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andyl - Member

I know this is a bit odd but I'm having a bit of a nightmare with my new boiler. I've got a Worcester Bosch 30CDI but it turns out I have too much pressure drop on my gas pipes for it to be commissioned. Having already thrown a fair wack at upgrading the exposed pipes there is no change. There must be something causing trouble under the concrete floor so I need all new gas pipes...or swap the boiler for the lower spec 30SI.

So if anyone is looking at a new boiler in the South West and fancies a cheap 30CDI that's done about 10 minutes then give me a shout as I'm really fed up with it all now

Posted 4 months ago #
edd - Member

Yes, about to install a new combi in my flat. Flat is in London but I can collect from the SW depending on where you are. How much are you looking for?

Edit: ps E-mailed you now.

Posted 4 months ago #
brant - Member

How much. Where from?

Posted 4 months ago #
totalshell - Member

what a load of bullocks.. who sold you that line.. the pressure 'drop' will be just the same with a 30si as it is with a 30cdi..
the working pressure drops due to the friction in the pipe therefore a larger bore is usually the req. however it may be that the pipe is blocked 22mm pipe will normally go for about 20 meteres before dropping the 1 mbar allowed
wb as your installer will tell you allow some fairly severe drops due to the nature of the gas valeves ( much above those permitted by gas safe)
contact wb and ask them to visit if the pipes are sized correctly and certainly in every case i have consulted them they have okayed the installation..

Posted 4 months ago #
Bear - Member

no strictly true the pressure drop will be ever so slighly less as it is rated a bit less (0.16m3/hr!)

Be very careful with that as the instructions state do not continue unless correct gas pressure is achieved. I would want it in writing before I agreed to that, but yes I have also heard them say that they will accept working pressures down as low as 14mbar.

Posted 4 months ago #
totalshell - Member

3 times i have had them check this in the resence of transco once on a 42kw and twice on 30si, asked wb to do the commission and they did, paperwork and all i think the lowest pressure was 15mb. the 40kw was only a metre from the meter and it was piped in 28mm. i cant see that the 0.16 will make any measurable difference to the OP though i would suspect that the pipe is restricted/blocked at some point if the distance is reasonable in 22mm. without the tech details though it'd be just guess work.
i think ( without my book to hand ) that too low a pressure would be NCS.. it certainly was on a new 28kw wb that i was asked to 'repair' by the local gas safe inspector as the original installer refused to work in the property..

Posted 4 months ago #
paulosoxo - Member

Worcestershire tend to struggle below 18. I'd not commission one that low though.

Can you not just re run the gas? Even if you have to run some outside. It's worth doing. I'm surprised your installer never picked this up sooner though.

Posted 4 months ago #
andyl - Member

Ahh Tootall, just the man.

Pressure at meter is about 19.6 at full power and Struggles to make 17.4mbar at the gas valve. Pipe work was all 22mm and now is a mixture of 28 and 22mm.

Currently have:

meter, 22-28mm, 90deg, 90 deg, <0.8m, 90deg, 1m, 90 deg, 1m, 90deg, 1.6m, 45deg, 0.3m, 90 deg.

Then 28-22mm and into the concrete floor where the route and condition is unknown. Hall way is 6m long, and then we have about 3m to the middle of the living room and then 3m to where I have picked it up under the living room floor.

Then I have in 22mm: 90 deg, 0.5m, 90 deg, 0.2m, 90 deg, 1.5m, 90 deg, 0.6m up into boiler.

Looking at the manual it states the 30CDI will take down to 18mbar but the 30Si will take down to 16.5mbar.

There is no mention of the total drop for the 30CDI (installer tells me it should be 1mbar) but the manual for the 20Si states 1mbar from meter to inlet and then 1.5mbar to valve allowing a total of 2.5mbar.

It was suggested to me that in retrospect the 30Si would have been a better choice due to the pressure drop. Or is this wrong and with either I will have to replace all the pipes?

So close to removing the whole thing and fitting some electric heaters and renting it out cheap to compensate for the crappy running costs of electric.

Posted 4 months ago #
paulosoxo - Member

First of all, and apoligies if you have said why, but why isn't the supply upped to 21mbar at the meter.

Have you actually worked the pipe sizing out to see what you should have?

Posted 4 months ago #
andyl - Member

Running outside is awkward. Lots of down pipes too close to the wall, stone steps to drill through and then the fun of drilling back through 0.7m wall under the boiler. Oh and it's about 17m round the outside.

Oh and it will require making an amendment to the listed building consent

Running through the house means me channelling out the concrete floor and making a channel and covering it with steel plate. But I am scared of hitting the central heating pipes. I know where some are but not in the middle of the flat.

I have just realised there is a big crack across the concrete floor in the hall. I wonder if the pipe is damaged there. Maybe it is worth getting a decent metal detector and digging up a few areas. It is as though there is blockage or crushed section somewhere. If only I had an endscope.

Posted 4 months ago #
paulosoxo - Member

If its buried in concrete, it'll leak eventually. Id just get rid now and be done.

Posted 4 months ago #
totalshell - Member

your nearly but not quite there.. the pressure drop over the journey ( meter to appliance should be no more than 1 mbar) you should start big and work down 28 to 22.

you have two issues i think .. firstly the working pressure at the meter isnt great.. get your gas supplier to check that ( its free) its not bad but not great

from your figs you have about 20m of installation pipework plus a dozen 'elbows ( which add to the length a half metre each) so that is why your drop is over the 1 mbar..

i know you cant do anything about the pipe in concrete but i'd put all the acessable pipe in 28 and avoid using fittings for the bends and bend the pipe instead..

this will bring the thing very close to 1 mbar i suspect and lift the 17.4 above the minimum for the boiler..

dont chuck the boiler .. this by the way is your installers fault not yours and it should be him working this out not you..

Posted 4 months ago #
andyl - Member

going to have a crack at working out the pipe losses myself. Wish I had looked into a while ago.

Ended up having to get Transco (or whoever they are now) out last week as the valve before my meter started to leak a small amount. Guy condemned all the pipework to the whole bank of meters (5 flats) as they had used galvanised steel pipes with cast iron elbows which had rusted away to paper thin in places. Holes were appearing as he undid the pipes. Took him a while to rebuild it all.

Posted 4 months ago #
andyl - Member

The original 22mm pipe they took out had bends instead of elbows but they removed it and fitted elbows and 28mm - so no change. I'll do some calcs and see if this is due to the elbows making it just as bad as the original 22mm.

Does it matter if the pipe drop is over mbar if the boiler is still getting >18mbar?

Also if I do dig up the floor and find the old pipe to replace it with 28mm then what precautions do I need to make when reinstalling it?

I would prefer to go through the flat as it will be a lot shorter and would cover it with a steel plate before fitting the flooring (laminate) over it.

Posted 4 months ago #
andyl - Member

Paul - not sure about the pressures. I'm not sure what is what to be honest as this is all new to me.

One more thing - when leak tested they picked up 2mbar after 2 minutes out of allowable 8mbar. I wasn't happy with any leaks tbh but I think this leak might actually have been due to the valve that has just been replaced. It was on the feed into the meter but no idea if the gas was leaking from the gas main side or the meter side. Even if the main fire valve I have right by the meters (not out in the road) was not fully open I don't see how it will affect the problem as surely the at meter reading would have dropped even more?

Ps thankfully no other gas appliances in the house. Reason I got the 30kw boiler was for the hot water. I briefly tested the shower and it was amazing

Options seem to be

1. dig up and replace the pipes
2. run a very expensive external route (don't like external pipes that can get knocked)
3. swap the boiler - if this is still an option?

Posted 4 months ago #
grantway - Member

Andy before you rip up your floor get them to disconnect the pipe starting from outside
your house and the disconnect the pipe before your boiler and get them to test the pressure

I take it you have the correct size of pipe work

Posted 4 months ago #
takisawa2 - Member

If you can email me a sketch of your pipe run, with the dia(s), I'll chuck it through our CFD software & see what that says. At least you'll have a theoretical figure. Might have to do some calcs to get it back to a pressure drop/time instead of a vol/time flow rate. I did some work on a domestic boiler a while ago, & the spec was 15-25mbar, but in some of the testing we found some areas at under 15mbar. You would be surprised how big you need to go to deliver a couple of litrs/min at 15mbar, despite nat gas density being a fair bit less than air. Also, when your dealing with pressures this low any deviation from a smooth path has a big negative effect. This crack across the floor doesnt sound good...

Posted 4 months ago #
tomlevell - Member

It isn't necessarily the installers fault as it depends on what gas pipe he could see/you told him about. Mind it sounds like you knew what was there and most was visible.

These are max lengths to produce 1mbar drop of either size ignorning bends as they don't have that much effect in smaller pipes but if your close to these max lengths then go up a size.

30 CDI 3.4m3/hr
Max length of 28mm copper (ignoring bends) = 38m

Max length of 22mm copper (ignoring bends) = 10m

30 SI 3.24m3/hr
Max length of 28mm copper (ignoring bends) = 41m

Max length of 22mm copper (ignoring bends) = 11m

So say you have 12m 28mm and 15m of 22mm then total mbar drop is 1.708mbar for the 30cdi.

The 22 is killing the gas flow rate.

Posted 4 months ago #
tomlevell - Member

Oh and if you went for a 24kw combi at say 2.45m3/hr

28mm = 73m
22mm = 20m

My example above would give you 0.723mbar drop.

If you have exact lengths and quantity of bends I can run it for you. Yes I can't be arsed to add all those bits up from up there.

Posted 4 months ago #
andyl - Member

using a general rule of 0.5m for a 90 deg elbow I have:

Old section 1: 6m of 22mm
New section 1: 7m of 28mm

Section 2 (bit unknown): 12m of 22mm

Section 3 (new bit): 4m of 22mm

Total before: 22m of 22mm
Total after 16m of 22mm and 7m of 28mm.

Bit general so maybe allow a reserve factor.

Is there really that much difference between 28mm and 22mm? That is huge!

and no, crack doesnt sound good. Not pointing any fingers either, just need to get it sorted and throwing cash and time to keep replacing bits is not conducive.

Posted 4 months ago #
tomlevell - Member

Yes the difference is quite large for gas. Theoretically you can go 28mm to 22mm and back up to 28mm if it makes it work. Bad practice to install new like that but to get you out of a hole...

0.5m for a bend is a rule of thumb that ers on the side of caution so best to run with that.

So 16m of 22mm and 7m of 28mm yes?
You have 1.67mb drop
0.184 on the 28mm and 1.486 on the 22mm
You need 18m 28mm and 5m of 22mm to achieve 0.937mbar drop.

I wouldn't install that though as it's not leaving much margin for error. 28mm from meter to boiler with last bit out of floor to boiler in 22mm giving more like 0.804mbar.

As said above WB might give you the green light to run and commission the boiler but not worth the installers head to do that without permission.

Oh yeah and copper buried in concrete without protection means you'll be replacing all your pipes one day. Might take 20+ years though from new...

Posted 4 months ago #
andyl - Member

I originally discussed making the new to the boiler (section 3, 4m) out of 28mm and cut a channel for 28mm but 22mm was used. When sorting the quote we also discussed making section 1 out of 28mm but this was then left until after the pressure drop was looked at. And yup then I ended up paying full whack for that bit to be changed as it had to be done on another day.

Tom - are those calcs based on 1mbar drop? What about the 30Si allowing for 2.5mbar? Surely the 22mm goes up to 27m for that?

Takisawa - cheers. Unfortunately it's the bit in the middle that's a big guess so I don't have a clue what the route is. Might have to pick up a metal detector and see if I can trace the pipe from where it enters the flat.

Posted 4 months ago #
andyl - Member

The existing pipe is wrapped in denso stuff at about 3 inches deep by the fire and just under the surface where it enters the flat.

What is the regs regarding depth and physical protection against nails etc? Don't seem to be able to get a definitive answer anywhere.

Posted 4 months ago #
DavidB - Member

Jesus Christ. I knew us IT types could speedwank but you gas fitters are in a different league!

Posted 4 months ago #
andyl - Member

@Brant - down in Brizzle. Don't have a nice Ti 29er demo lying around do you?

Thanks for the help guys, looks like the 22mm pipe was never going to work for that boiler. Even without knowing the exact route it must be in the region of 22-24m which exactly ties in with the loss I am getting. That should have been obvious to the installer from the outset IMO.

Posted 4 months ago #
tomlevell - Member

No regs and burying gas in concrete is bizarrely ok and denso will protect it.
Bury a mains water pipe in concrete and your for the high jump.

All based on 1mbar drop as this is what your allowed domestically.

Pointless excercise on the other boiler as it will be practically the same.

2.5mbar drop?
Too much drop officially but most boilers will work. BUT you have to commission as the manufacturers manual and if it says it won't work below a pressure then you don't do it.

Mine are based on a formula. The domestic gas guides from Corgi and similar (yes it's controlled by Gas Safe now but Corgi still produce books) give a table to aid those plumbers who can't use formulas and to be fair I'd not want to if I was out on the tools. Basically what I'm getting at is it sounds like you MAY have been badly advised and it's not hard to look at the table and realise that there will be a too greater pressure drop. BUT quite often it works as I see plenty of boilers running on 15mm pipe from older installations.
Has the plumber double checked the incoming pressure as this should be 21mbar?
I say MAY above as I don't know the conversations you had or how reluctant you came across in conversations about digging up the floor to replace the pipe etc.

Posted 4 months ago #
andyl - Member

He wants to run the pipe around the outside instead of me digging up the floors but the outside route is a lot longer and has quite a few nasty obstacles. including a gate, stone steps, enclosed area that is always damp and a listed consent issue.

RDA has just been cancelled due to bad weather so I think I might head in (living an hour away doesnt help) and investigate cutting up the floor from where it enters the flat. Funny you mention water mains as there is a water main somewhere around there but it's in some boxing in to the side so I think it goes straight down deep.

Posted 4 months ago #
andyl - Member

Good news....all finished!

I called Worcester after the advice above and they said they have amended the specifications and to get the installer to call them with the readings as they would allow what I was getting.

So...arrange for the installers to come back out and mentioned about getting the gas pressure turned up by the utilities people but it turned out that the guy that rebuilt all our meter pipework last week also replaced all the valves and regulators and set the pressures up at 21mbar and at full power the boiler was seeing 19 - 1mbar over what it needs.

I finally had my post boiler installation beer and curry that night! Thanks for all the help guys. I am now very, very relieved.

Posted 3 months ago #
bruneep - Member

Good news for you, no so good for those looking for a free boiler.

Posted 3 months ago #

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