Mains booster pump to increase shower flow rate from combi boiler

[JezW]

Nice calculator!

But a 7mm bore hose loses 0.8 bar? That seems very high!?

I think my current hose is longer than 1.5m as well..

 

[trojanhawrs]

Does seem high but it'd explain why you're getting such an increase by just dropping the shower head. Would suggest you've got somewhere between 1 and 1.5 bar dynamic at the mixer. The mixer is still likely throttling the flow to balance temperature so there's a good chance you'll get a flow close to your 12 with a less restrictive head. Let us know how you get on!

 

[JezW]

Just by dropping the shower hose actually! The flow is the same with the hose, and with the hose + head. New hose arrives tomorrow. Will report back!

 

[JezW]

New hose!

Cold (7c)
Flow out of the new hose, no head - 13.5LPM ! (must have some measurement error)
Flow out of the new hose, with head - 12.9LPM

Hot (approx 41c, ΔT = 34c)
Test 1: Flow out of the new hose, no head - 9.6LPM
Test 2: Flow out of the new hose, no head - 10LPM

So...what does this tell us?

1. The new shower hose is a good improvement on the cold
2. The shower head is having little impact
3. My cold water flow rate is fine

My boiler can supposedly produce 10.4LPM, so I guess this is about the best I can hope for then?

 

[Notch7]

Just ordered a large 11mm bore shower hose

where did you get your hose from?

my shower is a bit piddly as well (not combi just lack of head on cold water tank above shower head)

TIA

 

[JezW]

https://www.amazon.co.uk/dp/B01F3UL1PY?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

where did you get your hose from?

my shower is a bit piddly as well (not combi just lack of head on cold water tank above shower head)

TIA

 

[trojanhawrs]

New hose!

Cold (7c)
Flow out of the new hose, no head - 13.5LPM ! (must have some measurement error)
Flow out of the new hose, with head - 12.9LPM

Hot (approx 41c, ΔT = 34c)
Test 1: Flow out of the new hose, no head - 9.6LPM
Test 2: Flow out of the new hose, no head - 10LPM

So...what does this tell us?

1. The new shower hose is a good improvement on the cold
2. The shower head is having little impact
3. My cold water flow rate is fine

My boiler can supposedly produce 10.4LPM, so I guess this is about the best I can hope for then?

I'd say so yeah, a 30% increase is pretty good for 15 quid though!

 

[Johntheo5]

There obviously will be a pressure drop in the boiler plate heat exchanger but you should look for a restrictor in the boiler somewhere which you may be able to remove. As the mains temp starts rising then it would be nice to avail of the extra flowrate.
You will also get a LPM or 2 more maybe if you increase the combi HW temp to its max of 60C? as the cold% will increase and hot% decrease.

 

[JezW]

Hmm just did some more tests. Temp was around 41c.

Boiler temp set to 56c
Flow out of the new hose, no head - 9.9LPM

Boiler temp set to 60c
Flow out of the new hose, no head - same - 9.9LPM

The increase does seem good for the £££ spent. Although I'm wondering if I calculated the flow rate wrong with the previous hose!

What I'm annoyed about is this boiler is only a year old. Before choosing it, we checked the flow rate on the cold mains at the bath tap, and the kitchen tap. It was around 9LPM. I checked it again today. 8.5LPM out of the kitchen tap. So it didn't make sense to go for a 30kwh boiler at the time. But clearly I should have done! How is it possible that my shower can output over 13LPM on the cold, and the taps only 9LPM at the most.

So next time I need a new boiler...check every outlet in the house!?

 

[trojanhawrs]

Standard isolating valves have a reduced bore to calm the taps down a bit.

 

[Johntheo5]

Hmm just did some more tests. Temp was around 41c.

Boiler temp set to 56c
Flow out of the new hose, no head - 9.9LPM

Boiler temp set to 60c
Flow out of the new hose, no head - same - 9.9LPM

The increase does seem good for the £££ spent. Although I'm wondering if I calculated the flow rate wrong with the previous hose!

What I'm annoyed about is this boiler is only a year old. Before choosing it, we checked the flow rate on the cold mains at the bath tap, and the kitchen tap. It was around 9LPM. I checked it again today. 8.5LPM out of the kitchen tap. So it didn't make sense to go for a 30kwh boiler at the time. But clearly I should have done! How is it possible that my shower can output over 13LPM on the cold, and the taps only 9LPM at the most.

So next time I need a new boiler...check every outlet in the house!?

@muggles states that the boiler has a internal flow restrictor but I don't see any mention of it in the MIs, (above), no harm though to isolate the mains and remove the mains inlet to the boiler and check for any external restrictor, also check the isolating cock/valve at the boiler is fully open. Also check shower filters, if accessible,
While it won't help, maybe check the DHW flowrate, d.36, in the diagnostic parameters.