Combi Boiler and/or Megaflow

[JamesLeFeet]

We have an Ideal Minimizer (50,00BTU) and a Heatrae Sadia Megaflow CL170. Both are 12 years old. The boiler has always been unreliable and needs remedial action/rebuilding about every nine months - this is done by British Gas.

The house has 19 radiators and the system really struggles to provide hot water and central heating during cold spells. I know nothing about the technical stuff but I think the radiators will not come on if the temperature of the water in the Megaflow is below 57 degrees and if someone has a shower the temperature in the megaflow goes well below that for ages (maybe two hours) and if several people shower (separately) then the "hot" water becomes cool and we can forget room heating for the day. I suspect that the whole system needs to be replaced. However, ...

We are going to replace the boiler and a plumber has suggested a Worcester Greenstar 30 combi boiler. The write ups sound good but my basic question is: will the new combi boiler work efficiently with the Megaflow? Will we see any improvement in terms of hot water and room heating?

All advice, hints and tips gratefully received.

Cheers, James

 

[kevindgas]

I suggest find another plumber!
why would you have a combi and a megaflo?
heat only boiler + megaflo = good system
combi + solar tank = good system
combi + megaflo = ??????

 

[Agile]

Any combi boiler will work well with the megaflow if the installer knows how to fit them together.

The mere fact that you are asking here makes me think you must have doubts on his competence.

I am wondering what he is going to use the boiler's hot water for! Unless he needs 30 kW then that boiler may be over powered for the heating system which might need about 20 kW but you have not listed the sizes of each rad or described the house.

Your existing boiler is about 15 kW and from what you say may be underpowered or possible there is a problem with the pump or system design which means its full output is not reaching the points of use.

During colder weather does the boiler cycle on/off or is it firing constantly?

Tony Glazier

 

[JamesLeFeet]

Tony,

Thanks.

I think the boiler is underpowered but I also agree that there is probably something stopping what energy there is from reaching the megaflo efficiently.

The boiler does not work constantly and comes on and off even when the temperature of the water in the megaflo is way down on what is needed.

The radiators are a mix. Most of them are about 3'x2' single panel with a couple slightly bigger double panel. The radiators in the 3 bathrooms heat up when the boiler is heating up the megaflo. The other room radiators heat up when the megaflo temperature reaches the 57degrees. Most of the other room radiators have thermostatic valves.

The boiler certainly needs replacing and has been very unreliable and we have finally, finally, lost faith in it. Do I have faith in the plumber? Well, up to a point. He has done good work for us in the past. Our heating system seems to be hellishly complicated and I am just trying to set expectations (mine and my family's). As the megaflo and a new combi boiler will work together as you say then it seems to me that we should go ahead - any other problems (with the pump or valves) will then hopefully become obvious.

Regards,

James.

 

[BigBurner]

If you continue to use the unvented cylinder then a combi is a waste of time. Do want to get rid of the cylinder and have more space?

How many bathrooms? Showers?

If a straight boiler change go for the Broag oven vented boiler. It has integral weather compensation, so buy the outside temperature sensor. Superb.
http://www.avantarange.com/heating_boilers.html
Get either the 18v or 24v. 5 year guarantee.

PS
The Minimiser is just plain bad.

 

[kevindgas]

Any combi boiler will work well with the megaflow if the installer knows how to fit them together.


I am wondering what he is going to use the boiler's hot water for! ?

Tony Glazier

are you not contradicting yourself here?

why isn't the OP upgrading the existing HEAT ONLY boiler with a better HEAT ONLY boiler ?
seems the logical way to progress
interested in your responses as i'm willing to listen to reasonable arguement in favour of a combi which i still feel is wrong!

 

[BigBurner]

If you want to reheat the cylinder quick, you can attach the combis DHW circuit to the cylinder. The DHW outlet to the top of the cylinder and the return from the cylinder to the to the combi cold inlet (has to be a combi suitable for a hot inlet). Have brass pump on the return pipe to the combi with a check valve in front.

The cylinder heats in double quick time as it is using the plate heat X of the combi not an inefficient coil. The cyl' stat switches the brass pump. A cheaper direct cylinder can be used, saving about £130.

 

[DP]

Total figment of imagination. Result of brain that cannot reason.

 

[gas4you]

WARNING

If you want to take the advice of someone who is unqualified and has never fitted a boiler or unvented cylinder in his life, then go ahead and listen to Big Burner.

All his information is obtained from brochures and the internet, which you can do equally as well yourself. In both mediums, manufacturers are always going to paint their products in a good light. Just search his previous, outrageous posts on here and then see for yourself. The only posters that appear to agree with him are those that are him using a different 'alias' and talking to himself.

He can never offer any qualified reason for his posts and always comes back with some pathetic off topic slur against anyone who exposes his true incompetence.

 

[BigBurner]

Total figment of imagination. Result of brain that cannot reason.

Cheap to do fast to recover. What else don't you understand?
You are not even from Norwich.

 

[gas4you]

What else don't you understand?
You are not even from Norwich.

I rest my case m'lud

 

[Agile]

There is usually little price difference between a heat only and combi. If there is enough mains water flow and users for hot water then sometimes a combi is a good solution to feed the kitchen for example. However, a 24 kW combi would be adequate and suitably rated for the heating.

However, I have a suspicion the OP may have misunderstood the plumber who may be planning to get rid of the cylinder!

I still think the existing boiler would probably do quite well if its use was optimised.

If it really is under powered then it would be burning continuously during heating times and we have not had that confirmed. We had a comment about water heating which is not the question I was asking.

I will ask again in capitals!

DOES THE BOILER CYCLE DURING HEATING DEMAND ? If so what is the on/off times?

If it does then the pump or circulation is not removing the heat that the boiler is providing. Is pump on "2" or "3" ?

Is the system sludged?

Has the pump head been removed and the eye checked for debris?

I hope that all the major heating distribution circuits are in 28 mm or 22 mm ?

Tony

 

[mickyg]

I know of a couple of roads in a place with initials GO with the exact set up the OP has described, about right size house as well in hertfordshire. Don't remember the boilers being undersized though, but a while since I was round that way. Sounds like they just need a reliable replacement boiler. No point wasting money on combis etc.

Big Burners suggestion would work in theory, but manufacturers of both cyylinder and boiler would not allow it, so any warranty would be dust. I would also question whether it complies with building regs, I doubt it.

 

[kevindgas]

i see where your thought are Agile had visions of an install like Bird Brain was suggesting which sounds highly dangerous!

 

[JamesLeFeet]

OK chaps. Thanks for all your comments and ideas. It has been very useful. We are going for a heat only boiler with roughly double the power of the Minimiser. The combi idea was a complete mistake on my part. Sorry about that.