Can you help me? Combi boiler or condenser?

[Storm]

(I think a combi is condensing as well, but not sure what the other type is called)

We've had a few plumbers in, but they all have their own ideas, and no-one is in agreement, so I though I'd seek the advice of a random set of people who have no vested interest...

Our current set up:

Old boiler, cold tank in loft, hot water tank upstairs. Old pipework/ radiators. Very good water pressure downstairs, but we need a pump to run a shower as the pressure is not goos enough for a shower. Outlet for gas is too near back door, therefore illegal.

Suggestion 1 (suggested by 2 people):

Completely change system to combi boiler, bypass shower. Add new valves on radiators. Take out tanks. reckon about £2000. More expensive to fit, cheaper to run.

Suggestion 2 (suggested by two others):

Just change old boiler for a new condenser. They have said the old controls will still work, but some boilers have controls on them that we could use instead. Use some sort of flue kit to take the emissions away from the door.

Those in favour of the combi seem to think our old controls need to be replaced, those in favour of new condenser say they're ok. One said our old hot water tank and our central heating would stop the new boiler working as well, so switch to combi.

My own concerns about a combi: is there enough pressure (2 taps/ shower running etc.) if the boiler breaks down we are left with no hot water. But if we just change the boiler, we are left with old controls/ hot water tank and these could break down at some point.

Can you give me any advice at all?? I realise that you have not seen our central heating, but I have no clue, and seeing as no two plumbers agree I don't really know who to ask...

(Also they all disagree with which boiler to get, and one said they are all much of the same - but the more you pay the better quality you get - and just to go for whatever is on offer and gives the best deal at the time).

Thanks!!!!!

 

[Bartdude]

What sort of house do you have? How many people live there? How many bathrooms?

 

[Storm]

3 bed semi (quite big), 2 adults and 2 children. 1 bathroom.

 

[tamz]

A combi would make sense but don't expect to be able to run 2 taps at the same time with any other than the biggest ones. It will be cheaper to run as you are not heating and storing water you don't need. But if it develops a fault you have no heat or water.
The pump for the shower can be taken out (unless it is one with a built in pump) and you will get a better shower without it.
Combi boiler controls are slightly different to the ones you have. They only need a 1 channel programmer where at the moment you will have a 2 channel and they can use programmable roomstats, wired or wireless.

If you like the stored water and back up capacity of an immersion there would be nothing wrong in just changing the boiler for a regular or system boiler. The flue thing they are talking about is called a plume kit which enables the fumes part of the flue to be easily extended to a more suitable location.
Depending on how old your existing cylinder is or if it is lagged, you may consider changing that too. Newer ones have a faster reheat time. You could fit any new controls you like. Keeping the existing ones keeps the price down.

If you don't have a room stat you should fit one regardless of what type of system you go with. Same for thermostatic radiator valves.

All makes of boilers do what they say on the tin. They will all do their job. Some are slightly more reliable than others or built to a better quality and the cheaper ones generally cost more for spares. Buying expensive does not mean it will not break down. They will ALL break down at some point unless you are VERY lucky.

 

[Storm]

Thankyou. We are leaning towards getting a combi (a bigger one) as long as the pressure for the shower will be ok. Is there any way of checking that the pressure for the shower will be ok without a pump on the new system, before taking the 'risk' of swapping over. Currentky without the pump, the shower is just a trickle of water, even though pressure everywhere else is good. We like the idea of a combi, but don't want to regret it.

 

[Storm]

Argh! I'm so confused! I'm reading so much that seems to say that traditional systems are better. we have old radiators and pipes and that this could cause problems in a combi system with leaks etc. We have an old badly installed cylindar. Should we just replace the lot with a conventional system????

 

[raymondo68]

Hi Storm

This is always a tricky one. A couple of things you may like to consider. Do any of your neighbours have a combi boiler? If they do ask how it works for them. For a house your size a combi boiler would not be over exerted.

Combi boilers come in a range of sizes expressed in terms of power output 24Kw is just about the smallest with 40kw about the biggest. There are two factors that will determine whether or not you should install a combi

1. The water pressure available in the main, this can only really be tested by fitting a pressure gauge to an outlet. A good heating engineer will have one and should really check this unless their local knowledge tells them that the water pressure in the area is good.
2. Just as important is the flow rate of the water. You can get a good indication of this by timing how long it takes to fill a 2 litre milk bottle or similar with the cold mains tap fully open. If you have an outside tap (This is usually also connected to the main). You should repeat the test with that tap
fully open at the same time.
If it takes 10 seconds to get 2 litres then you have roughly 12 litres per minute (2 x 6 = 12) This would represent the bare minimum for a combi . If it is much faster i.e 5 seconds or less then a combi will give you a decent shower without the need for a pump.

When installing combi's I try to encourage people to have an electric shower fitted. This partially overcomes one of the main problems with the combi, that if it breaks down you lose everything.

The reason it is difficult for anyone to advise you with total clarity is that these are issues of personal preference.

If you cannot stand the thought of only being able to have 1 hot outlet open at any one time then DO NOT get a combi. If the pipes that feed your radiators are imbedded in a concrete floor think very carefully before getting a combi.

If you do go with a conventional system you should carefully consider replacing the cylinder is the one that you have is probably quite inefficient.

I hope this has been of some use, I really do think that asking neighbours and friends locally is the best way forward.

Good luck

Raymondo

 

[tamz]

If you are replacing with a combi your old pump, valves, cylinder and cold tanks will be disconnected and removed. Your water pipes will then be changed around a bit to give you a mains pressure supply to all your taps, hot and cold. The same as the cold at your kitchen sink is at the moment. The only parts of your old system that will remain are the radiators and pipes feeding them.
Don't believe all that is written about leaks all over the place due to higher pressures. Yes the pressure is higher but no higher (less in fact) than the pressure going through your plumbing pipes. If the odd leak does appear it shows up almost immediately is usually no more than a drip and is easily rectified. (Can be a bit different if you have pipes buried in concrete)
Usual places for leaks are around old rad valves or compression fittings. Sometimes if your radiators are in a really bad condition it can cause them to leak. (not all old radiators are in bad condition).
A decent installer will have a look at your existing pipes and radiators and see what condition they are in. If he thinks they are bad he will not risk pressurising it.
Don't worry too much about it. You just need to put it into perspective. Millions of people fly in planes every day and very few crash!

Generally any combi, even a 24kw, will give a decent shower as good as or more powerful than a pump providing the mains pressure and flow are adequate.
The force of the shower from a combi is determined by the incoming mains pressure which can be anything up to 6 bar +.
Bigger combi's will give a greater flow rate.
A 24kw combi will give around 11.5litres/minute with a 30º temperature rise (ie if the cold coming in is 10º and your shower is 40º), a 28kw around 13.4l/min, a 30kw around 14.4l/min and a 37kw around 17l/min. The flow rates will rise by 15 to 20% in the summer as the incoming water is warmer so you can add cold to it.
There is not much difference in the flow rates between makes of boilers of equal output.

Before you decide on a combi get the installer to check the pressure and flow on your mains supply if you think it may not be up to it.

 

[Hankers]

Hi Storm, I made the change to a combi in November and to be totally honest its been fantastic. Previously I too had an open vented system with a 1.5 bar pump to the showers, it was ok like that, but now there is no comparison the shower is much much more powerful. I put in a 35 KW boiler but you shouldn't need one that big with just one bathroom. If there is one downside its that the bath takes a bit longer to fill but it really is only a minor point. All I need now is to see my first gas bill and hope that its less!

 

[Bat502]

Hi Storm, I made the change to a combi in November and to be totally honest its been fantastic. Previously I too had an open vented system with a 1.5 bar pump to the showers, it was ok like that, but now there is no comparison the shower is much much more powerful. I put in a 35 KW boiler but you shouldn't need one that big with just one bathroom. If there is one downside its that the bath takes a bit longer to fill but it really is only a minor point. All I need now is to see my first gas bill and hope that its less!

What make did you get and what are the most reliable? DO NOT get a IDEAL ISTOR HE260/325. Very very bad. Had nothing but problems 2 years after new install with a new build.

 

[Jamie Banks]

Hi

just a quick one been looking into this myself also be aware that there are 2 types of condensor boiler:

Condensor combi (sealed system no tanks) and condensing regular (Y plan with tanks)

Have a look at both and work out which is best for you

 

[Bernie2]

Hmm!

One of the problems with a combi is the hot water flow rate. In a very simple way. Imagine you had a metre long piece of metal pipe and you put cold mains water in one end and heated the pipe with a blow lamp.
Now the water has only got a metre to travel before you want it to come out hot. So you need a lot of heat and the hotter or the bigger the pipe the more heat you need.

It's also why the amount of heat for the central heating side of a combi, is usually well within the amount of heat needed for the hot water. And why the bigger the boiler the more water you can get out of it.

So you may get something like a 12kW combi but the central heating would only require say 10kW. It is possible to get it wrong of course and get a boiler that is enough for the hot water but not enough for the central heating. So you have to get some idea of what you want first.

A condenser is more about efficiency than anything else. If you stick your hand in a boiler flue plume its hot I can tell you. But the heat goes to the atmosphere and is wasted. So a condenser recirculates it and makes it heat more of the water in the boiler. That's basically it. It isn't that simple though its just to give you some idea.

So basically a condensing boiler either of a standard type or a combi is supposedly more efficient than the none condensing boiler. And if you have got a lot of taps you need a big boiler and you need the water pressure and flow coming into the house to be able to supply all those taps as combi boilers usually have a lot of resistance and require decent pressure to push the water through it.

There are plenty of websites that will tell you more about combi's. But as has been said you are very reliant on them for both heat and hot water and they are reputed not to be all that reliable and so I would advise you to get yourself one of the repair plans going about.

 

[oiley]

Some would argue that with the new regs coming in soon then looking forward you could do worse that putting in a condensing system boiler with a new twin coil unvented cylinder, them you will have high pressure for shower etc, lashings of hot water and a cylinder which could be connected up to a renewable source such as solar in the future,

 

[Storm]

Oiley:

Is that a 'system boiler'? They latest guy suggested going down that route - ie pressurised system, but retaining the shower pump and hot water cylinder and having to heat water each day. Sort of half way between the combi route and what we have. BTW I have asked the neighbours - they do have combis and like them, so I know our mains pressure should be fine.