Using Combi as a multi-point

B

BigBurner

It is quite common to use combis as multi-points by loop the CH flow & return pipes together.

To get a decent flow rate a high flow combi is needed and these tend to cost. An Andrews WHX42 NG External Water Heater, giving 17 litres/min, costs £575.75 Including VAT, the internal model is more expensive. A 42kW W-B approaches this flowrate but costs far, far more. But some budget combis like Heatline can do lower flowrates and still be very cost effective.

When used as a multi-point water heater do most modern combis leave the 3-way valve alone? That is, if the valve fails it doesn't matter as it doesn't not move and always in the DHW position. The CH controls don't matter either. This makes them more reliable when used as DHW only water heaters.

The problem with the competitive Andrews multi-point, is that it is not condensing, so will use more gas to run. Although being fitted outside is a great bonus. They do have inside models.
 
Sponsored Links
B

BigBurner

It is quite common to use combis as multi-points by loop the CH flow & return pipes together.

A multipoint would be a few hundred quid cheaper than a combi! :LOL:

A low flowrate multi-point (9-10 litres/min) and an equiv combi? The combi is equiv if buying a budget model.

A non-condensing Main fan flue @ approx 9-10 litres/min is: £418.30 Including VAT
An equiv condensing Heatline is: £477.05 Including VAT

£50 more for using less gas.
 
Joined
8 Feb 2004
Messages
8,022
Reaction score
148
Location
Wolverhampton
Country
United Kingdom
A decent combi is around £700 - £800 and a multipoint will probably be around £400 - £450. :rolleyes:

You have a unique view on heating your home. :D
 
Sponsored Links
Joined
5 Aug 2008
Messages
5
Reaction score
0
Country
United Kingdom
yeah, why get a combi of your not gonna use it for heating. Waste of money chap. Main do good multipoints, cheap and easy to fit.
 
B

BigBurner

yeah, why get a combi of your not gonna use it for heating. Waste of money chap. Main do good multipoints, cheap and easy to fit.

You are missing the points. In flowrate vs flowrate at the bottom end, the combis is more expensive, but uses less gas so is a better buy. reliability of the combi should be high as it is stuck in DHW mode permanently.

Some non-condensing Rinnais reach the meter capacity while an equiv flowrate condensing combi would be well within.
 
Joined
24 Jul 2003
Messages
24,294
Reaction score
1,416
Location
London
Country
United Kingdom
A combi wouldn't be condensing as much, if at all, depending on the model, in DHW mode. Seen any figures?

IME where combis are used as multipoints, some bright spark usually comes along later and has a "brilliant idea" that a towel rail or something could be run off it.

Some combis exercise the DV periodically, others would still fail even if CH weren't used, and others forbid having no CH circuit.
But yes, they all make better water heaters than carppy Main/Chaff multipoints (which don't even have a temp sensor).
 
Joined
4 Aug 2005
Messages
14,792
Reaction score
2,841
Location
Yorkshire
Country
United Kingdom
i was talking to Morco about their band C combis. "Why are they not band b?"

"Because there is no point in the small dwellings our stuff is fitted where 6kw heats them up in 30 minutes the boiler doesn't normally condense and they usually don't condense on hot water either"

The gassaver (Alpha and now others) is probably the best way to get a condensing boiler to operate efficiently on hot water but at a price which you could buy a solar panel for which should give a much better preheat to the cold mains. (for example bigburner space allowing one of those black painted used copper cylinders in a box tilted to sun buti would use the cylinder as a vented store and pass mains through the coil before the combi/water heater but avoid diaphragm flow sense models. Vaiilant only approvepreheat up to 38 degrees so tmv adjusted to this recommended.) Naturally i am preaching to the converted but we can band these things about. Iron sharpens iron.

I don't have a problem with using a cheap combi as a water heater however.

OTOH my flat underneath with it's Brittony IIT hasn't had a diaphragm for 5 years I cleaned the pilot jet about 4 years ago the lodgers never complain about hot water performance. I have owned it for 9 years it was probably 10 years old before I bought the place.

When I fitted central heating 9 years ago I decided to leave it in and used a regular boiler which in that time has only required an OH stat.

At the same time in another flat I fitted a Eurocombi available then for £350 from MkM as a special.

It has given grief about twice a year and required a new prv a new diaphragm and serivice kit for DV. But it is still soldiering on the usual fan relay problems haven'tkicked in yet the fan is still going strong. But for sure it will fail before the Brittony II and the regular boiler.

In the other flat I fitted a Buderus combi. never had a hiccough from it. Absolute dream boilers. I did install a magnaclean with that one.

My retired Mexico is soon to be displaced by a buderus regular boiler.
 
Joined
24 Jul 2003
Messages
24,294
Reaction score
1,416
Location
London
Country
United Kingdom
I recently had to THROW AWAY a Chaff Water heater. It was leaking water and gas and corroding.
It was SOO unreliable, I'd had to put a thermocouple in it, in about 1993. I remember because it was a secondhand thermocouple.
This troublesome thing was in the house when she bought it, in 1972.
Combis last 40 years, don't they??
 
B

BigBurner

A combi wouldn't be condensing as much, if at all, depending on the model, in DHW mode. Seen any figures?

However the combi heat exchangers are larger anyhow, so more efficient. Look at the specs. The temp rise and flowrate and max gas consumed. The condensing combis us less gas than the non-condensing multi-points.

I have seen combis as multi-points in small companies, supplying two toilets and kitchen. Fitted by the local plumber who probably had never heard of Rinnai, and picked up a cheapo combi at the local merchants. They worked well and were cheap.

Some combis exercise the DV periodically, others would still fail even if CH weren't used, and others forbid having no CH circuit.
But yes, they all make better water heaters than carppy Main/Chaff multipoints (which don't even have a temp sensor).

One of the reasons I created this thread was to gain some insight into the control of some combis. One which leaves the 3-way valve alone (if it seizes or fails, so what!) and only uses the DHW controls is going to be very reliable as a multi-point. Even a budget combi thas does not use the CH side will be reliable enough.

One Main multi-point is forced flue with temp control. The controls are similar to a heating only boiler. I think they still make an electric-less heater too, which is very reliable being developed over 40 years.
 
B

BigBurner

Combis last 40 years, don't they??

Depends on the make and its quality. I can see an Atmos lasting 50 yrs. I recall the old Ascot multi-points lasting 40 years. They fitted many in flats with warm air. They tended to need a diaphragm about every 5 to 8 years.
 
B

BigBurner

i was talking to Morco about their band C combis. "Why are they not band b?"

"Because there is no point in the small dwellings our stuff is fitted where 6kw heats them up in 30 minutes the boiler doesn't normally condense and they usually don't condense on hot water either"

They have secondary condensing heat exchangers I believe.

The gassaver (Alpha and now others) is probably the best way to get a condensing boiler to operate efficiently on hot water but at a price which you could buy a solar panel for which should give a much better preheat to the cold mains.

In a commercial situation, like a kitchen, where the multi-points are used because stored water cannot deliver the hot water over say a 2 hour period, using a gassaver makes economic sense when using a com,bi as a multi-point.

(for example bigburner space allowing one of those black painted used copper cylinders in a box tilted to sun buti would use the cylinder as a vented store and pass mains through the coil before the combi/water heater but avoid diaphragm flow sense models. Vaiilant only approvepreheat up to 38 degrees so tmv adjusted to this recommended.) Naturally i am preaching to the converted but we can band these things about. Iron sharpens iron.

Most people don't have the space and would not like a large box with a cylinder in the garden. Fine if space is there.

At the same time in another flat I fitted a Eurocombi available then for £350 from MkM as a special.

It has given grief about twice a year and required a new prv a new diaphragm and serivice kit for DV.

The Ariston Eurocombi was a dog! The newer non-condensing Ariston Microgenus is reliable combi. I have had one for 6 years and hasn't missed a beat. The heat exchanger does not require cleaning it is so clean in the burner box, looking like new. I keep the CH on near max temp, which prevents any condensation occurring inside. I bought it because at the time it was the smallest combi in physical size to fit in a cupboard.

Not what I would have liked in quality, but surprised me big time - and it was not cheap at the time, but very highly specced with integral filling loop, by-pass valve, etc. It has an electric 3-way valve and standard Italian parts inside. Simple to work on, but I have not done anything to it yet. I may flush the system out and fit a filter on the CH.

The fan is noisy, the only down side, but in a cupboard it is not that much of an issue.

In the other flat I fitted a Buderus combi. never had a hiccough from it. Absolute dream boilers. I did install a magnaclean with that one.

Parts and service may be an issue with them as W-B want to phase them out of the UK market. I am not impressed with the 500 range. 600 looks fine. Those I have seen were a little too noisy for me. In German/Holland they tend to have basements for boilers so noise is not that much of a problem.
 
Joined
26 Jun 2004
Messages
64,233
Reaction score
4,661
Location
London
Country
United Kingdom
I see quite a few Biasi combis connected as a water heater only. They are little more expensive than a good multipoint and have far greater efficiency.

In spite of what Chris says, they are pretty fully condensing on DHW as the return is only at about 45°C.

Most installers just remove the stat loop and link the two CH pipes. Its not necessary to link the CH pipes as there will never be any flow to them as the diverter rests in the DHW position. I remove the diverter motor from the valve to prevent any fault arising.

I have also seen some combis fitted as system boilers as they are the same price or less. In that case the DHW pipes dont need to be connected. Some manufacturers say ( wrongly ) that the DHW pipes should be pressurised although if you analyse the situation its not of any advantage.

Tony
 
B

BigBurner

I see quite a few Biasi combis connected as a water heater only. They are little more expensive than a good multipoint and have far greater efficiency.

That is because Rinnai, etc do not import the condensing models to the UK. The sooner they do the better. Energy prices are rising like a kite and people want economy and are prepared to pay.

One Rinnai model just goes over the 6 cu metres/hr of the gas meter. If it was condensing it would be well within.

Rinnai are now importing smaller cheaper units, the 16i and 16x (x mean externally mounted - outside). These do around 10 litres/min in flow. The compete with Main and Chaff. I would rather go Rinnai, although some Main and Chaff models are super reliable.

Most installers just remove the stat loop and link the two CH pipes. Its not necessary to link the CH pipes as there will never be any flow to them as the diverter rests in the DHW position. I remove the diverter motor from the valve to prevent any fault arising.

Stat loop? Do you mean the room stat link at the terminal strip?

Do not link the CH pipes? You mean cap them off. I would link them in case there is flow for any reason and the pump is then moving water.

Removing the diverter motor. Would the maker back up the warrantee?

I have also seen some combis fitted as system boilers as they are the same price or less. In that case the DHW pipes dont need to be connected. Some manufacturers say ( wrongly ) that the DHW pipes should be pressurised although if you analyse the situation its not of any advantage.

I see no benefit in running the cold mains through a combi with a plate heat exchanger.

Many combis are cheaper than system boilers for the equiv output. Can the diverter m,otor be removed and the 3-way valve set at the CH only position. Would the makers go along with that?
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Top