Combi and ongoing running bath problems

[rundwald]

I moved in to my house, a 3 bed linked detached in 2002, and we had the kitchen revamped. The previous owner had two heating units in the kitchen, one for the central heating, another under the sink for instantaneous hot water by gas. (The house originally was heated by warm air). In place of two units the designer’s agent installed a combi boiler for which here are some details.

Protherm 80e

Flow rate @ 30 deg C temperature rise ….11.2 l/min
@35…………………………… 9.6 l/min
Minimum water flow……………………….2 l/min
Max/min supply pressure……………………6/1 bar
Full technical details are at

http://www.postimage.org/image.php?v=gx1mujcr

The boiler has never seemed particularly good on the DHW side, and that applies especially to running a hot bath and various things have neen done to make matters more satisfactory

10/11/05 replaced air in expansion vessel
28/11/05 replaced faulty plated
15/12/06 service note “pressure vessel may require recharging, not very good”.
12/02/07 re-pressurised expansion vessel, cleaned prv
18/02/08 replaced DHW diaphragm.

None has been particularly effective. We can only run a bath at a very slow rate, no more than a 10 deg twist f the taps beyond which water runs hot and cold.

We recently consulted a local engineer, who suggested that a power flush (£450) might be the solution, but also that the boiler was likely inadequate for us.
We are the two occupants and as well as DHW the boiler serves

2x26" double radiators; 2x33" doubles; 1x63" single; 1x44" single;
1x26" low level that goes under kitchen breakfast corner. double will grille on top; hated towel airer 600x1150 mm. Inch measurements are mine and rough; the metric one is from the handbook.

The bath is immediately above the kitchen where the boiler is situated, so I do not think there is a long run to contend with, if that is relevant.

In your opinions are his suggestions valid ones?. The power flush is expensive for us, and even more expensive is a new boiler at around £2200. That is if a new boiler would even be practical, seeing the current one is built in to a cupboard type casing, and from my research quite slim line.

 

[Agile]

Your kitchen designer was hardly a heating enginner!

They fitted one of the cheapest models and not a well known make either.

The only problem you have is that you will not live within the limitations of a basic power boiler.

A combi is well suited to runing a shower but not very good at filling a bath very fast.

You could have a hot water cylinder fitted for about £800-£1800 or completely free start using showers like most of the population of Europe.

Tony

 

[rundwald]

As I said the house was originally warm air so there's mo where to put a cylinder and there also is no storage tank.

Anybody else like to comment?

 

[Agile]

When I said a cylinder, that could either be an unvented mains powered cylinder or a vented cylinder supplied from a cistern.

In this world you dont get anything that you dont pay for. In your case you paid for a cheap basic boiler and thats what you have to live with unleyy you pay to upgrade it.

Probably 96% of combi boilers in London are only the basic 24 kW and their users all get used to using them within their limitations, mostly by having showers for which they work well.

Tony

 

[rundwald]

When I said a cylinder, that could either be an unvented mains powered cylinder or a vented cylinder supplied from a cistern.

In this world you dont get anything that you dont pay for. In your case you paid for a cheap basic boiler and thats what you have to live with unleyy you pay to upgrade it.

Probably 96% of combi boilers in London are only the basic 24 kW and their users all get used to using them within their limitations, mostly by having showers for which they work well.

Tony

So to be clear you think neither the power flush will be any good at all, nor a higher output boiler? yours is the only way round the problem?

 

[Agile]

Nothing you have said implies it needs a power flush.

You can check the temperature rise and the flow rate to see if its working according to the specifications.

A new boiler could be a more powerful one giving about 50% more flow rate but thats not a gigantic change!

A storage combi will fill a bath to a fair depth very quickly.

Tony

 

[Master of None]

I think the Vailant EcoTec is probably one of the slimmer compact boilers on the market and are available in high Kw models and mine fits in a 50cm wide 36cm deep kitchen unit.

 

[mehran]

get a water heater, the rinnai do a 20 l/m that can go inside or outside.

then use you combi for heating only

 

[rundwald]

......
You can check the temperature rise and the flow rate to see if its working according to the specifications.

A new boiler could be a more powerful one giving about 50% more flow rate but thats not a gigantic change!

A storage combi will fill a bath to a fair depth very quickly.

Tony

Thanks for further reply. How do I do the check?
You say 50% is not a gigantic change
I have never heard of those: are the cylinders mentioned earlier the same?
How do they manage to fill so quickly?

 

[DP]

Runwald, what is the flowrate from the hot tap. Take a bucket and a stop watch. With hot tap running full force, collect water in bucket for 15 seconds. Measure quantity of water in bucket and multiply by 4. This should be just under 10l.

Also take temperature reading of incoming cold water and hot water at the tap. Record both. If cold water is 10 degrees, hot should be 45 or more. If you are not getting this temperature rise, suspect gas line is undersized (quite common)

Do not think you will need a power flush. This is based on fact that system is new and unlikely to be sedimented so soon.

Post back. Will attempt to guide you through your problems.

 

[rundwald]

Thanks

based on fact that system is new

If that makes a diffidence, only the combi is newish, 6 y.o.; the c/h part is quite a bit older and installed by previous owner in place of warm air.

 

[bengasman]

these are horrible boilers, apparently sold by builders merchants some time ago. cheap, nasty, poorly designed and the company that made them is no more. taken over by glowworm who appear to make very little effort in supporting this make.
get rid of it, you are throwing good money after bad

 

[rundwald]

I am now coming round to biting the bullet and having a new boiler fitted together with an Aquadial Combicare scale reducer. (we are in an exceptionally hard water area). To fit in the limited available space a Flexicom 30CX has been recommended. According to a lot of sources the 35 deg rise flow rate is 12.3 l/min, rather than the Protherm's 9.6.
However somewhere in DIYnot forum the rate is quoted as 11l/min.

I am confused. Which is correct, or is it more complicated?

 

[DP]

Remaining with the facts and not deviating to what is good and what is bad, 80 would stand for 80000 btus which will deliver 9.5 liters of what ONLY IF the gas line is correctly sized (often times it is not) and the flow rate is as specified.

OP, could you measure the amount of water flowing from the hot tap over 15 seconds, multiply that by 4 to give you the flow rate. It should equal 9.5l. If you are able, check the cold water temperature and also the hot. At 9.5l flowrate, temperature rise should be 35 degrees as it says in the spec. If you try to increase the flowrate, temperature rise will be less. That goes for all combi boilers.

For the time being forget power flush and forget new boilers.

 

[Agile]

According to a lot of sources the 35 deg rise flow rate is 12.3 l/min, rather than the Protherm's 9.6.
However somewhere in DIYnot forum the rate is quoted as 11l/min.

I am confused. Which is correct, or is it more complicated?

Like a lot of things in the world some manufacturers seem to get away with over stating their products specifications.

Those figures are the boiler performance! A couple of degrees is lost in the pipework on the way to the bathroom.

So the 35° temperature rise becomes 33°. But if the water coming in is only say 4° then the bath temperature then becomes 37° which is not enough for most people.

So at this time of year a 20 kW combi will only give about 11 li/min at the temperature most people want to shower at. As a bath will also lose a degree or two the situation gets even worse.

Youhave been asked to measure the existing flow rate. You have chosen to ignore this request which would enable us to better assess your situation. Instead you have apparently chosen to have a boiler fitted which is not only a not very good one but a model which will give you little improvement!

I am intreagued where you are with water that you say is "exceptionally hard". Can you tell us?

Tony