Broag Remeha Avanta Plus 39c Combi Boiler / Low Pressure

[maddernj]

I have recently had one of these installed after reading about the great flow rates and reliability. After a few weeks of use I am not sure i am getting the best from it, I know its a pressurised system but the washing machine running or the toilet being flushed really impacts the shower. To give you some back ground its installed in a 3 bed semi with 9 Rads and Underfloor heating covering about 18m2. I had a new water main when installed so have 22mm pipework from the road into the garage (where the boiler is installed).

Should the pressure drop so much am I being unrealistic ?

Looking through the paperwork the HW flow rate was measured @ 13L/min, it currently sits @ 1bar.

As a side issue I am not convinced the underfloor heating pump is working either (or it runs silent with no vibration) so think the boiler is having to pump the HW round this as well.

Any Ideas ?

Thanks

[Ricky_M]

The performance of the Hot Water is dependant on the flow rate of the incoming cold main.

Just because it is 22mm doesn't mean it is a suitable supply.

Did the installer check the flow rate before he installed the combi?

[maddernj]

Yes and as my HW flow rate was written up as 13L/min after installation I don't think that is the problem, but I know nothing about this I am open to suggestions

[dirkgently]

maddernj said:

Yes and as my HW flow rate was written up as 13L/min after installation I don't think that is the problem, but I know nothing about this I am open to suggestions

The hot water flow rate may be 13lpm but if the main will only supply 13lpm you wont achieve that rate if any other outlet is open. It would appear on the face of it to be another badly specified system.

[maddernj]

Ahh I see, how do you check the mains pressure ?

don't worry found the part on plumbworld for £11,

What's considered Low ?

Edited by maddernj on Monday 20th June 15:31

[dirkgently]

maddernj said:

Ahh I see, how do you check the mains pressure ?

don't worry found the part on plumbworld for £11,

What's considered Low ?

Edited by maddernj on Monday 20th June 15:31

Forget about pressure its flow that you require. my kitchen tap supplies about 22lpm and I wouldn't dream of installing a combi on that flow rate if I didn't want issues.

[maddernj]

Ahh I see, so if i stick a 1lr jug under the tap and time it (Say 5 secs to fill and multiply by 12) that should give me my flow rate ?

[dirkgently]

That will do.

[maddernj]

Just noticed 22lpm and you would still get problems with a combi boiler ? That's 1ltr per 2.5 secs (ish) ??

Why do combi boilers always promote pressure as the main factor and not mention the flow rate with regards to usability ?

Wish we had stuck with a System setup now.....I knew nothing of this before !

[Arthur Jackson]

maddernj said:

Why do combi boilers always promote pressure as the main factor and not mention the flow rate with regards to usability ?

Because they would only sell them for very small houses or flats which is, after all, what they are good for.

[maddernj]

Flow rate is about 25L/pm in my very unscientific test, ergo should it be that if a 2nd appliance is drawing cold water it halves ?

[dirkgently]

Unfortunately you may have to get use to the fact that no one can use other appliances when someone is in the shower. If it's any consolation you have purchased a good boiler.

[cjs]

+1. It's one of the downsides of a Combi, they do not work well in a multi room family home, ok for a flat or small house with a couple of occupants.

I live on my own and have to make sure I do not do a load of washing whilst I take a shower.

OP, do you have a proper thermostatic shower mixer?

[maddernj]

A proper one ? its just a Bar with two controls....To be fair the drop in pressure is not terrible just noticeable. I guess all of the advice we were give up front about combi's saving space etc etc etc was just smoke and mirror's. I am just annoyed that when I spoke to 3 plumbers and said I wanted a central heating system where I will not notice the drop in pressure all said combi and only 1 offered the system as an alternative but was about £1.5k more expensive than the others.....drat !

Also just noticed on the website that the 39c can be converted to a system boiler, which is handy for when my girls grow up and I extend the house in the future....bonus !

Edited by maddernj on Tuesday 21st June 09:55

[cjs]

You do get far better shower pressure from a Combi than you do from a conventional tanked system, as long as you have a good water main. A tanked system would need a 'power shower' pump to achieve similar results.

Plus you never run out of HW, you don't need to have water tanks taking up space, you don't heat water you will never use.

[LFB531]

cjs said:

You do get far better shower pressure from a Combi than you do from a conventional tanked system, as long as you have a good water main. A tanked system would need a 'power shower' pump to achieve similar results.

Plus you never run out of HW, you don't need to have water tanks taking up space, you don't heat water you will never use.

Sorry cjs, have to disagree. As a letting agent looking after about 200 combi boilers, I think they're a disaster and mostly pre-programmed to pack up on a Friday afternoon just before a Bank Holiday. Has been better since we have gone the Worcester only route for replacements as parts are available off the shelf. Give me a decent system set up with an unvented tank and back up immersion any day of the week. No need for shower pumps, fast recovery and in a hard water area, the tank will last much longer.

Sorry, rant over!

[dirkgently]

cjs said:

You do get far better shower pressure from a Combi than you do from a conventional tanked system, as long as you have a good water main. A tanked system would need a 'power shower' pump to achieve similar results.

Plus you never run out of HW, you don't need to have water tanks taking up space, you don't heat water you will never use.

Sorry but this is the sort of talk that has gotten the OP where he is. Without knowing the site conditions and the customers requirements it is impossible to suggest a system.

[andy43]

dirkgently said:

cjs said:

You do get far better shower pressure from a Combi than you do from a conventional tanked system, as long as you have a good water main. A tanked system would need a 'power shower' pump to achieve similar results.

Plus you never run out of HW, you don't need to have water tanks taking up space, you don't heat water you will never use.

Sorry but this is the sort of talk that has gotten the OP where he is. Without knowing the site conditions and the customers requirements it is impossible to suggest a system.

He's actually correct making that statement. But as you say, it doesn't apply here.
If the dynamic mains pressure is good, and flowrate is good, a combi would work. Static pressure tells you nothing really. 22mm incoming supply is good, but if the street supply is hopeless, as here?, it's possibly pointless.
If the mains isn't up to it OP would be better off with a vented cylinder and header tank, with a shower pump. You could still have the combi, splitting the heating side in two to do rads and the shower cylinder. Rest of the house relies on the hot water side of the combi.
An unvented cylinder still relies on the water main for performance, so will still go flat as a fart when two taps are on together. An accumulator (we have one, so I'm obviously an expert ) would work with a combi or an unvented, storing water under pressure to be used when the mains can't keep up.
eta I think combis are the boiler equivalent of a washer dryer - too much all in one box.

Edited by andy43 on Wednesday 22 June 11:21

[cjs]

LFB531 said:

cjs said:

You do get far better shower pressure from a Combi than you do from a conventional tanked system, as long as you have a good water main. A tanked system would need a 'power shower' pump to achieve similar results.

Plus you never run out of HW, you don't need to have water tanks taking up space, you don't heat water you will never use.

Sorry cjs, have to disagree. As a letting agent looking after about 200 combi boilers, I think they're a disaster and mostly pre-programmed to pack up on a Friday afternoon just before a Bank Holiday. Has been better since we have gone the Worcester only route for replacements as parts are available off the shelf. Give me a decent system set up with an unvented tank and back up immersion any day of the week. No need for shower pumps, fast recovery and in a hard water area, the tank will last much longer.

Sorry, rant over!

What's there to disagree with, everything I said is fact. I never said that Combis were reliable.

[cjs]

dirkgently said:

cjs said:

You do get far better shower pressure from a Combi than you do from a conventional tanked system, as long as you have a good water main. A tanked system would need a 'power shower' pump to achieve similar results.

Plus you never run out of HW, you don't need to have water tanks taking up space, you don't heat water you will never use.

Sorry but this is the sort of talk that has gotten the OP where he is. Without knowing the site conditions and the customers requirements it is impossible to suggest a system.

Everything I said is correct, I was just reminding the OP of some of the benefits his system has given him. I am not saying his system is the correct one for his requirements (see my earlier post)