Ideal vogue poor hot water supply

[ash1212002]

We've just had an ideal vogue c40 combi fitted which has a hot water flow rate of 16.4L per min

Prior to fitting the boiler the cold water flow rate was measured at 18 litres per min

Looking at the digital readout the boiler is showing that the dhw flow rate is approx 12 litres per min when the hot tap is ran at the basin

When running the hot water tap from the bath it's slower!

The plumber is stumped any ideas?

I've noticed this evening, the cold inlet supply pipe to the boiler, the plumber has fitted an isolation valve, could this restrict the boiler from operating to it's maximum hot water rate?

 

[CBW]

Is the isolation valve full bore or reduced? Also what size pipework is feeding these outlets?

 

[ash1212002]

Is the isolation valve full bore or reduced? Also what size pipework is feeding these outlets?

It looks like a reduced bore isolation valve

The basin taps are 15mm

Looking under the bath, the hot pipe is 22mm but reduces down to 15mm to the bath tap

 

[CBW]

It looks like a reduced bore isolation valve

- won’t be much help, cut it out or change for full bore.

The basin taps are 15mm

Looking under the bath, the hot pipe is 22mm but reduces down to 15mm to the bath tap

Should be all 15mm usually.

 

[ash1212002]

- won’t be much help, cut it out or change for full bore.

The basin taps are 15mm



Should be all 15mm usually.

The plumber will be around tomorrow, so will instruct him to change it to full bore

So any hot water pipes that are 22mm should all be changed to 15mm?

Will that improve the hot water flow rate to the bath and basin taps?

 

[CBW]

Should see a marked improvement on the flow rate yes.

 

[ash1212002]

Should see a marked improvement on the flow rate yes.

Fingers crossed, will report back... Thanks

 

[Emit]

Silly question where was it measured. Was it near the point we’re the cold feed to the boiler is. Eg outside tap giving 18lpm. Yet pipe to cws giving 12lpm restricted. Then you fit a boiler on that pipe that gives 12lpm. It’s basic **** really. 22mm to bath was norm back in the days when on tank fed and I’m guessing this might be a boiler conversion? and reducing to 15 won’t give more flow it only reduces the time it takes to get a slug of cold water from cold to hot through a pipe. Basically 22mm pipe will hold more cold water than a 15mm pipe.

 

[Madrab]

So any hot water pipes that are 22mm should all be changed to 15mm?

Will that improve the hot water flow rate to the bath and basin taps?

No.

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The boiler's documented HW output is usually set as an absolute maximum @ a 35Deg rise and in perfect conditions. Real world performance is rarely the same.

It can all be influenced by mains water pressure, mains water temperature, the desired HW output temperature, length of pipework, bends, valves, types of outlets, etc.

Your plumber needs to look at all of that.

When the boiler was commissioned, what did the installer benchmark it at?

 

[Emit]

No.

=====

The boiler's documented HW output is usually set as an absolute maximum @ a 35Deg rise and in perfect conditions. Real world performance is rarely the same.

It can all be influenced by mains water pressure, mains water temperature, the desired HW output temperature, length of pipework, bends, valves, types of outlets, etc.

Your plumber needs to look at all of that.

When the boiler was commissioned, what did the installer benchmark it at?

Disagree .. read my post and argue all you want. If you think modern day mono mixer taps etc use 15-22mm inlets then let me know. Most common fault over the years with say a 24kw combi on old 22mm to the bath was a customer complaining in winter the bath hot is crap at full rate.

 

[Madrab]

Most common fault over the years with say a 24kw combi on old 22mm to the bath was a customer complaining in winter the bath hot is crap at full rate.

Invariably I don't argue in other people posts, I just use facts and let people do with them what they want and I certainly don't dive in aggressively in an open forum, been here too long for that.

Fitted many a combi boiler where there is an older 22mm hot water supply to the bathroom without any significant drop to the output in temp or flow.

A combi boiler with a certain input will raise a certain amount of water (L/Min) by a certain amount (target 35Deg Rise). In summer the mains cold water will be warmer therefore giving hotter water at the outlet than say in winter when the mains can be more than 5 deg colder. That is why, especially with smaller combi's, it takes an absolute age to fill a bath and even longer in the winter as the temp at the outlet is colder and then people turn the hot water tap down to raise the temp, unless you are running a large boiler with a higher delivery. Most med input boilers suffer from poor flow when filling a bath, moreso in the winter, it's a well known failing of combi boilers.

We all know that normal ISO valves and flexi pipes can reduce flow, though their impact is usually only seen where the mains pressure is low and yes there shouldn't be a normal ISO valve on the inlet to a boiler, that's just downright silly but that wasn't the question. In my experience whether it's 15mm or 22mm, the hot water at the outlet will be at much the same temp and flow unless the pipe runs are miles long and uninsulated.

Where the mains flow and pressure is more than adequate though then normal ISO valve's and flexi pipe's impact are normally reduced when they are fitted just before the outlet. They can usually deliver more than enough flow to supply a sink or basins mixer or a shower, especially where modern monoblocs and showers invariably have narrow water ways, aerators or water saver/flow reducers fitted.

All this is academic though and doesn't change the fact that just changing pipes from 22mm to 15mm wont recover the 5L/Min loss the OP is seeing IMO, there are lots of other factors that need to be looked at.