poor flow rate, am I missing something?

[fingertight]

Hi guys

I have fitted 2 Worcs 37CDI's recently, and I have noticed that the hot flow rate hasnt changed compared to what I took out (very old vaillant and a ferroli).which is crap compared to what it "states" in the brouchures.. gas rates fine.

Outlets averaging 9 to 10 ltrs a min..should be way more? Cold inlet pressure and flows have been fine....is it all a gimmick or do you guys notice a marked improvement in these type installs.

 

[Boilerman2]

A Combi Boiler can only put out the flow rate that goes in i.e. if the cold water inlet gives 9 -10 Ltr/min (pretty poor) then the best supadoopa combi in the world will only put out 9-10L/min (still pritty poor)

 

[BingoBongo]

did you check the mains before installing? and i dont mean try holding back the cold with your hand

 

[fingertight]

Cheers Boilerman, I agree, thats bread and butter stuff, fisrt thing I look at, cold inlets have been fine... both jobs 16ltrs a min cold according to worcs flow cups.

I cant ignore stuff like that lol (dog with a bone) as at this stage im thinking the clients who request these boilers might aswell go for a 30kw combi and save money or go all out and pay for unvented?

 

[Gasguru]

Is this post a windup

If you're serious it's quite worrying.

You might like to remove the flow limter fom the boiler.

 

[fingertight]

Gas guru,

Thankyou. Its not a wind up...Whats more this was never touched upon even at worcesters own training courses?

I have contacted Worcs Technical...and I am worried...becasue the flow limiter cannot be removed and never should be removed if it is possible..no adjustments needed...just a straight forward 13ltrs per min on average as soon as boiler is switched on. So either Worcs tech dont know their own product or you have your wires crossed?

A dangerous engineer is the one who holds questions back when he is unsure

 

[Gasguru]

Hot water flow rate is determined by...

Static pressure in the street main

Service pipework and fittings


The boiler manufacturers fit flow limiters within the boiler to prevent high volumes of users phoning up their technical teams complaining of poor performance due to excessive flowrates...more than the boiler can cope with.

If your inlet pressures/flowrates are poor removing the flow limiters can often help the situation.

Just because a particular boiler states it will heat water at such and such rate it is still entirely dependent on there being sufficient pressure and flowrate at the boiler inlet (and sufficiently sized gas pipework).

You seem to be implying that fitting a higher output boiler should automatically allow the water to flow at the stated flowrate regardless of incoming water pressure/flowrate.

You can remove the flow limiter. Who is telling you it can't be. Perhaps the strainer is simply blocked. If training courses went into the basics of water pressure and flowrate you'd be there all year. Worcester technical (along with many others) often don't know their own products...expecially the CDi's.

You will find (with accurate thermometers and flow measurement...many Weir gauges are very inaccurate) that boiler manufacturers tend to be cconservative with their performance measurements.

I hope you are measuring the dynamic (or working) pressure at a particular flowrate.

 

[fingertight]

Thanks for the info Guru.

I Probably wouldn't attempt to remove the limiter (void warranties etc?)

sufficient incoming cold flowrates are obvious...Im curious because like I say, incoming cold has been fine on last 2 installs, gas rates smack on on maximum demand..but flow rates no different to an ecotec pro 28?

It was Worcester Technical that told me the limiter must never be removed (the lad said it cant be removed anyway?) He said you would get too high a rate then (20ltrs+) screaming through the H.E if was removed.

Im probably going to go go with a belt and braces approach from now on and if a client specifically requests an impressive flow rate and asks me for recommendations, Ill choose thermal store (Ecotec plus 937?) i've never fitted a 937 or alike but it has to have better flow than non store boilers?

or unvented if the monies there.

 

[simond]

Fingertight wrote

I have contacted Worcs Technical...and I am worried...becasue the flow limiter cannot be removed and never should be removed if it is possible..no adjustments needed...just a straight forward 13ltrs per min on average as soon as boiler is switched on. So either Worcs tech dont know their own product or you have your wires crossed?

I assume you realise that the figures published for combis are 35deg temp rise (Delta T) but most are set up to deliver at 42C Delta T. With water mains delivering between 5C -10C this time of the year, a 35C temp rise would not be enough.

Therefore the published hot water figures for the 37CDi (15.1 litres per minute) are for a temp rise that the boiler is not set up to give in normal circumstances, just under 13 litres per minute is what can be expected. A Vaillant is set up the same.

When I go to boiler quotes for my company I take a flow cup and demonstrate the flow rates each version will achieve in real terms, this way the customer knows what to expect.