Worcestor Bosch highflow 400 electronic RSF - Potential Prob

[aelitaman]

I hope this is the forum to ask, I have a Worcester Bosch Highflow electronic 400 combi boiler, the installer did a mains pressure test and flow rate test before installation and said all was fine. It is meant to have a flow rate of hot water of 18 litres a minute. Because of a thread on another forum about bath filling times, I decided to measure the flow rate. The temperature setting for the water is set to lowest (55C) on the boiler. I get 12.5 litres/min on the kitchen tap which is the same level as the boiler and I only get 6 litres per minute on the bath hot water tap which is 2 storeys higher (about a 9m rise).

When I turn the cold tap on at the same time as the hot water is on it just about doubles the flow so I assume the mains pressure is fine. The funny thing was when I had the boiler installed 2005 the first day when the installation was finished the hot water absoultley gushed out of the tap, much to my surprise as I was expecting there to be a difference moving from a gravity system to a combi. Next day it was lower, I noticed it and I raised the issue with the installer who said it was the water pressure into the boiler and that it fluctuates due to demand in the locality.

So to the experts on here. Seeing as I am getting so low flow rates compared to spec and I had, when first used the system, seen much higher flow rates do you think that something in the boiler has failed? or do I need to add a secondary pump?

Also I know WB service offer a fixed fee service but also the option of paying just over 200 quid and this covers parts that may be needed if a fault is discovered, so a recommendation as to whether I use this option would be appreciated.

Thanks in advance.

 

[picasso]

at 55c your boiler will give 18 litres per minute for 4 minutes, when the thermal store is depleted its just a 24kw combi boiler giving about 10 lpm, so its sounds like your boiler is about right.

 

[aelitaman]

It does not even give 18litres for 10 seconds let alone 4 mins. Also I thought it had a 60 litre tank that was drained at 18 litres per min and top up at 10litres per min at the same time meaning a net drain of 6 litres per min so it should do 18 litres for 10mins.

 

[Agile]

You seem to be missing the point!

All the water into and out of your boiler comes from the mains.

You seem to have had a thick plumber to fit your boiler who does not know the difference between an open pipe flow rate and a dynamic flow rate and could not even notice the effect of a three story building.

If the flow rate has diminished since new then the inlet filter may be blocked. That should have been checked on the annual services.

You have had the boiler serviced annually haven't you?

Tony

 

[0161coop]

Has the flow rate slowly declined over the last 4 years or hs it been the same since day two?

Do you live in a hard water area?

 

[aelitaman]

Yes the Map of the UK water hardness says I live in an area that is hard to very hard. The kettle furs up very quickly. So do the ends of the taps.

I noticed the initial drop after the first day, now I think about it over those four years the bath takes twice as long to fill now than before.

 

[Agile]

I may be wrong but I thought that yours was a storage combi with the DHW being heated by flowing through a tube through a heat store which contains system water.

If that system water in the store is too hot then its quite conceivable that lime scale can be deposited on the inside of that tube.

Having said that its not a common problem that we hear about.

In a hard water area it would be normal to fit a magnetic water conditioned on the mains water input to your boiler.

Tony

 

[aelitaman]

Agile, I am no expert so please take this as just somebody who is not experienced with boilers but has read the manual to see if he could work out if anything is wrong.

How I understand the 400 works is that it has a 60L water store that is constantly kept to temperature. Then when you turn the tap on, the hot water is delivered in as short a time as posible from this heat store. The burner fires up and heats the incoming mains water to temperature and this is added to the heat store at the rate that the boiler can heat it to the correct temperature.

The name "HighFlow" for the boiler was used because flowrates above mains flow rates can be achieved because the water store can be drained quicker than the mains water can be heated to temperature meaning that you get a certain amount of time at higher flow rates and when the tank is depleted it will work at a flow rate that is equivalent to the capacity of the boiler to heat mains water.

To answer your previous question yes it has been serviced regularly by a local chap. This time I think I will pay WB to come and give it a service and check.

 

[Agile]

What you have said is in essence what it does!

I am trying to establish exactly how it achieves that so that I can consider id the DHW side has become scaled up. But I need a boiler engineer to confirm this.

If it has then that would explain some or most or all of your problems.

I doubt that the Worcester fixed price repair would cover descaling or replacing the secondary heat exchanger.

Tony