VaillantEcotec plus 837

[Wizard007]

I had this boiler installed by a suitably qualifed plumber in October 2009. If we are only running one hot tap the pressure is great and I understand that if we run another hot tap, we will naturally suffer a reduction in flow. The issue I have is that if whilst running a hot tap, I open a cold tap, the flow reduces by approximately 65-70%.

I have spoken to Vaillant who have said that the reduction should only be 10% and I have spoken to the Plumber who says that a reduction in flow should be expected and that there is no other problem. I'm now going to try and rectify the problem myself!

If somebody could help me understand what my be the problem, or if I am just being awkward, then I would be very grateful!

John

 

[plumbnuts]

You only have one water main comming into your property (I assume). When the hot tap is open you will get the full flow through the boiler to the tap. When you open a cold tap in addition the water flow will be split between the two and therefore the flow reduced to both taps. There are other factors to be taken into account such as flow resistance and frictional loss through the boiler. However, I would expect you to lose far more than 10 percent as stated by Valliant

 

[Wizard007]

Thank you!

Anything to help me lift the confusion is good! I do have one mains feed to the house as you assumed.

Is there anything that you would suggest I do to solve or lessen the problem or would the only solve be a bigger boiler or a return to a traditional boiler and a hot water tank?

 

[gas4you]

What pressure and flow rate do you have on your cold mains static and when another tap is running?

 

[Wizard007]

I'm afraid I don't know the water pressure.

I did specifically say to the plumber that fitted the boiler that I wanted the water tested to ensure that we had sufficient pressure and he said categorically on more than one occaion that there was no need to test the pressure.

He said "You have enough pressure to fill the tank in the loft and therefore you have more than enough pressure to power a combi-boiler".

Is it a possibility that we do not have sufficient mains pressure for this type of boiler?

 

[Wizard007]

Sorry,

further to your question, the plumber has suggested fitting a bladder to the mains to help the problem...is this an option?

 

[gas4you]

Sometimes it is obvious to the experienced eye whether you have enough flow or pressure for a combi, but if going for a larger model, you will need to have it checked before a decision is made about whether it is suitable.

His statement about filling the tank in the loft is the biggest load of ball cocks I've heard this month

 

[Wizard007]

Thanks Dave

I have my hands on a 'flow cup'? which I will be using to guage the pressure this evening.

I will post my results tomorrow and then any suggestions would be warmly received!

 

[gas4you]

The flow cup will only measure flow, not pressure.

You will need an absolute minimum of 16 l/min to have made this boiler worthwhile fitting.

 

[Wizard007]

Having used a flow cup for the first time, I'm even more confused.

Two of us measured the flow to make sure that the reading was reasonabley accurate...

Kitchen cold Tap - 16 litres per minute
Kitchen Hot Tap - 18 litres per minute
Kitchen hot tap with utility room cold tap running - 6 litres per minute.

Main Bathroom bath cold tap - 18 litres per minute
Main Bathroom bath Hot tap - 12/13 litres per minute
Main bathroom bath hot tap with main bathroom sink cold tap running - 5 litres per minute.

I am now completely confused! Any added expense is not an issue for me as I just want this sorted. What I do want to avoid is throwing good money after bad!

Help!

 

[Agile]

I did specifically say to the plumber that fitted the boiler that I wanted the water tested to ensure that we had sufficient pressure and he said categorically on more than one occaion that there was no need to test the pressure.

He said "You have enough pressure to fill the tank in the loft and therefore you have more than enough pressure to power a combi-boiler".

I do have to say that anyone who fits boilers who says that is a complete nupty!

Very unfortunately, and embarassingly, many people fitting boilers really dont have much idea of the technical aspects of boilers, pressure and flow.

I can accept that you dont know the difference between flow and pressure ( although its only GCSE level science ). What I cannot accept is that anyone involved in our trade should be working if he does not know the difference.

Whats needed is a dynamic flow measurement before fitting any combi boiler. Your nupty did not do that.

From your open pipe measurements your flow is not that dire. You will probably be able to live with that if you learn not to turn taps on fully.

Its not a simple problem to resolve! The basic solution is to upgrade the supply pipe from the street. Thats usually costing about £800-£1600 !

Other trade people on here will not all agree with me but the lack of knowledge shown by your installer makes me come to the conclusion that he was not fit for the job and should contribute significantly towards solving the problem which he did not recognise as a result of his lack of knowledge.

Because we dont always get given the full story, can you confirm that he is an identifyable tradesman who is gas registered and doing your installation in the course of his normal business?

Alternatively we often find that people have used someone they see working for another company on the street and then get them to do a "cash" job "on the side" when in reality they are not qualified, capable or insured to that that work.

Tony

 

[harold5]

you need to measure the working pressure as well. the second you open the cold tap you are dropping the pressure/flow to the boiler,combined with the frictional loss through the boiler you get poor performance.
could be a combination of poor pressure,small bore water main/pipework ,stop tap not open fully. other option is to fit service valves on cold outlets and restrict them down.