Concerned that boiler is undersized

[evets51]

Hi, I have started to become concerned that the boiler I had installed in February is undersized.

Background is we moved into a new house last October, its off-grid and has LPG gas heating. The boiler was 20 years old and seemed to use a horrendous amount of gas (£300 / month through winter). So we replaced it with an Intergas condensing system boiler. I knew nothing about boilers at the time - the guy who came and installed it didn't do any power measurements, he just replaced the one we had with a similarly-powered Intergas boiler (18kw).

Its currently a 5 bedroomed house, approx 2150 square foot including a conservartory. 20 year old wooden framed double glazing that doesn't have a huge gap between the panels so isn't particularly efficient I think. I topped the loft insulation up to 270mm myself.

When it was built (and the old 18kw boiler put in) it was a 4 bedroom house with no conservatory. The previous owners had put in the conservatory (with two radiators) and a large extension over the double garage, holding the master bedroom, wardrobe and en-suite (1 large + 1 small radiator, 1 heated towel rail). So in total there are 4 extra radiators + a heated towel rail compared to when the house was built.

We only used the boiler for a couple of weeks back in February, then we were away on holiday and then it wasn't cold enough to put the heating on. Now its got cold again I've noticed that the house takes a long time to warm up. As an example, last night I had the heating controller set to 16 degrees overnight, then at 5:30 set it 19 degrees. When I came downstairs to the room the controller / thermometer is in (lounge) at 6:30 it was reading 17.5 degrees only - so 1.5 degrees warmer than when it came on at 5:30. When I left the house at 7 it was still only reading 18 degrees and the boiler was going full tilt. That's when my 1 year old gets up and 18 is about the minimum temperature I want the house for him.

I've noticed the radiators are never really "too hot to touch". At their hottest I can hold them for about 10 seconds before it starts to get uncomfortable. Was at someone else's house this weekend and noticed that I really couldn't hold the radiators for more than a second. Other concerns are, it takes half an hour after the heating comes on for the radiators to get even that hot. Also I cannot run the hot water and heating at the same time - I have to run the hot water from 5:00-5:30 so there's enough in the tank for a hot shower when I get up, if I set the hot water to come on at 6:00 when the heating is running there's just no hot water.

I've also spoken to another guy in my area who had the same pattern house as mine, and who has had exactly the same extensions done. He mentioned that when they had the bedroom built, they had to get a bigger boiler as the old one was struggling ...

I've been trying to get hold of the installer who did this work for some time now to no avail (old problem, he seemed to do a good job at the time but is practically impossible to get hold of). I'm starting to feel highly annoyed as I paid over £2k for this install in February, and I'm starting to think I'm going to have to have a new one installed. I guess my questions can anyone confirm my suspicions that my boiler sounds underpowered, and is there any likelihood I have any comeback against the guy who installed it given that I was naive enough at the time to not even ask about power of the boiler etc? Thanks.

 

[WHPES]

You can do the calcs yourself here:

Replacement Boiler Size Calculator

18kw does sound somewhat on the small side for a 5 bedroom house.

 

[evets51]

Thanks. Based on two walls at 8 metres, two at 14 metres, two floors, detached, cavity walls with insulation, pitched roof > 75mm insulation and leaving the rest as default, in the south east, that's telling me 14.5kw which seems on the small side?

 

[kay-jay]

i agree.
he should also have updated the heating plan to allow for independent heating and hw.

 

[evets51]

Hmm, well when it isn't that cold outside and the house gets up to temp quickly, as it was a few weeks ago, then I can have hot water on at the same time as the heating. It only seems to be when the boiler is going at full power for hours at a time to try to heat the house up, that if you put the hot water on at the same it fails to get hot.

 

[Gray0689]

Is the house badly insulated aswell
But does sound small

 

[jtsplumbing]

You may find that the system is dirty, or the pipe work is undersized, also get someone in to make sure that the boiler is set up to poduce the right amount of heat and is getting the right amount of gas .

 

[evets51]

Well the loft has approx 300mm insulation in all of it except one central section approx 4 metres by 0.75m which has 100mm insultation then carpeted boards on top, for walking around. It was built 20 years ago and looking at breaks in the walls in the loft, I can see glass-fibre wool between the wall cavities so I'm pretty sure it has cavity wall insulation. There are a lot of windows - mostly 20 year old wooden double glazed which aren't the best but at least its not single glazing. The front room has a floor to ceiling metal framed, double glazed patio door which again, I'm sure would be better as a modern uPvC one but I can't see it making that much difference.

The conservatory used to be open-plan to the kitchen, and it was a heat sink - when it was really cold last Feb we could never get the house above 14 degrees so we had modern uPvC A rated doors / windows put in to seal it off. We now keep those closed in the cold weather and don't and turn the radiators out there off at the TRVs. So overall I'd say it isn't quite up to new build standards but isn't bad?

 

[evets51]

You may find that the system is dirty, or the pipe work is undersized, also get someone in to make sure that the boiler is set up to poduce the right amount of heat and is getting the right amount of gas .

Thanks. There was a power flush done when the boiler was installed, and I've read through the instruction manual to check that the pump is set to its maximum possible power output, and the central heating water temperature is set to maximum (90 degrees, it was set to 75 degrees until last week when I first became really concerned, that's when I upped it). But yes, my next step is to get an independent party out to assess it.

 

[DirksPlumbing]

How can one make judgements about heating up times without knowing about the structure of the house? 18kW sounds pretty OK. If there is large heat storages like massive stone walls and even worse concrete flooring then that is still an amazing performance.
Especially if you take in consideration that such a type of house might take weeks to reach its temperatures stable.
As for the radiator temperatures have a rethink about condensation and high temperatures.

Just as a hint, changing the boiler without ensuring that the radiators are capable of dealing with the (new) system temperatures might not have been the best idea.
Add on: And of course pipework is capable.

 

[WHPES]

Think I figured out what's happening - pipework layout needs looking at.

Trouble is I'm used to fitting boilers in stone built properties here with no cavity wall insulation.

The bottom line is that you need to do the calcs before making a decision.

 

[chris watkins]

First things first, what is the boiler thermostat set to ?? make sure it is set to maximum (80deg C water temp).

 

[evets51]

First things first, what is the boiler thermostat set to ?? make sure it is set to maximum (80deg C water temp).

Its set to 90 (was 75 until last week). 90 is the maximum.

 

[jtsplumbing]

Settings seem high, Pump on max, could be pumpimg to fast through boiler , should be no need to run boiler at 90! what about radiator size's are they big enough for the rooms ? why not pick up a rad chart from a plumbers out let and see what the total heat output is on all your rads, allow 3Kw for hot water , if the boiler never switch's off and is not getting up to temp then you have a problem !! and it could be costly.

 

[TFGplumbing]

Hi, I have started to become concerned that the boiler I had installed in February is undersized.

Background is we moved into a new house last October, its off-grid and has LPG gas heating. The boiler was 20 years old and seemed to use a horrendous amount of gas (£300 / month through winter). So we replaced it with an Intergas condensing system boiler. I knew nothing about boilers at the time - the guy who came and installed it didn't do any power measurements, he just replaced the one we had with a similarly-powered Intergas boiler (18kw).

Its currently a 5 bedroomed house, approx 2150 square foot including a conservartory. 20 year old wooden framed double glazing that doesn't have a huge gap between the panels so isn't particularly efficient I think. I topped the loft insulation up to 270mm myself.

When it was built (and the old 18kw boiler put in) it was a 4 bedroom house with no conservatory. The previous owners had put in the conservatory (with two radiators) and a large extension over the double garage, holding the master bedroom, wardrobe and en-suite (1 large + 1 small radiator, 1 heated towel rail). So in total there are 4 extra radiators + a heated towel rail compared to when the house was built.

We only used the boiler for a couple of weeks back in February, then we were away on holiday and then it wasn't cold enough to put the heating on. Now its got cold again I've noticed that the house takes a long time to warm up. As an example, last night I had the heating controller set to 16 degrees overnight, then at 5:30 set it 19 degrees. When I came downstairs to the room the controller / thermometer is in (lounge) at 6:30 it was reading 17.5 degrees only - so 1.5 degrees warmer than when it came on at 5:30. When I left the house at 7 it was still only reading 18 degrees and the boiler was going full tilt. That's when my 1 year old gets up and 18 is about the minimum temperature I want the house for him.

I've noticed the radiators are never really "too hot to touch". At their hottest I can hold them for about 10 seconds before it starts to get uncomfortable. Was at someone else's house this weekend and noticed that I really couldn't hold the radiators for more than a second. Other concerns are, it takes half an hour after the heating comes on for the radiators to get even that hot. Also I cannot run the hot water and heating at the same time - I have to run the hot water from 5:00-5:30 so there's enough in the tank for a hot shower when I get up, if I set the hot water to come on at 6:00 when the heating is running there's just no hot water.

I've also spoken to another guy in my area who had the same pattern house as mine, and who has had exactly the same extensions done. He mentioned that when they had the bedroom built, they had to get a bigger boiler as the old one was struggling ...

I've been trying to get hold of the installer who did this work for some time now to no avail (old problem, he seemed to do a good job at the time but is practically impossible to get hold of). I'm starting to feel highly annoyed as I paid over £2k for this install in February, and I'm starting to think I'm going to have to have a new one installed. I guess my questions can anyone confirm my suspicions that my boiler sounds underpowered, and is there any likelihood I have any comeback against the guy who installed it given that I was naive enough at the time to not even ask about power of the boiler etc? Thanks.

The inter-gas Boilers only operate at 70% of the total output standard from the factory 12.6kw for the 18kw SB. Now I think you can ramp them up to the full output however I am not sure; But I will be when I do their installers course on the 19th of this month haha 🙂

 

[evets51]

The inter-gas Boilers only operate at 70% of the total output standard from the factory 12.6kw for the 18kw SB. Now I think you can ramp them up to the full output however I am not sure; But I will be when I do their installers course on the 19th of this month haha 🙂

Its quite confusing. The instruction manual gives you a chart on how to set the maximum power output, I've been through this. From memory, the setting "70" on the LCD display actually equates to 85% power output - and that is the maximum you can ramp them up to. I've certainly been through that bit of the book and ensured that it was set as high as it could go.

 

[petercj]

I've got a 18.5 kw condensing boiler running 13 radiators in a house that sounds to be a similar size to yours.

By any formal sizing calculator the boiler is undersized, however, it hasn't caused me any problems yet.

If the house is completely cold on a winter's day, then it takes longer than it should to raise the temperature with all rads on.

However, once the general temperature in the house is up to a comfortable level, the boiler tops up the heating as required - I do have Thermostatic Radiator Valves on most of the radiators.

If your system is clean, then make sure your radiators are balanced, and that your pump is right for the job, and in good working order.

Boilers sometimes stop and start as they ramp up the temperature, but once up and running, make sure that your boiler isn't cutting out for some good reason that needs looking at.

Condensing boilers run at their most efficient when working hard, so maybe your engineer was thinking of that.

But if you do the maths, it does sound as if your boiler is on the small size for the job.

Try turning off some of the rads so that you only have 10 working, and then see how the system performs.

If he's not responding to your communications, I suggest that you send him a Recorded Delivery letter explaining the problem and your concerns, and ask him to come and look at the system and let you have his explanation for the issues raised.

P.S. My boiler is set to 75c.

 

[evets51]

So having had someone round to have a look, I'm told that its most likely a circulation problem. He put the boiler on "installer mode" and we turned the room thermostat way up, supposedly it should run on high power constantly like this. It slowed down / went to trickle after just 5 minutes, whilst the radiators were still not all that hot to touch. He explained this will happen when the difference between flow and return is not high enough to warrant full power, basically the system thinks the heat isn't going anywhere .. We walked round and many of the radiators were hot at the top on the flow side, but lukewarm / cool on the bottom.

So apparently I have a microbore system, but the two rads in the conservatory (which were done as an extension a few years ago, before I owned the house) are on regular-sized copper piping. The power flush I had done when the boiler was installed was done from one of those conservatory rads. The engineer explained that if the piping had been installed properly, those conservatory pipes would have come off the main trunk of piping and the power flush should have worked fine. However, if it had been a cowboy job (his words) they could have teed off one of the microbore radiator pipes - in which case this could have caused the power flush to not work properly. His suggestion was to do another power flush, but this time to do it by connecting up to the pipes which come directly out of the boiler to ensure that the full pressure of the flush gets through the system. Apparently if that fails then my next option would be to have the pipework replaced which sounds expensive ....

Any thoughts on that? - it sounds reasonable to me but then I know nothing 🙂. Thanks in advance for any replies.

 

[jtsplumbing]

A lot of the power flushing machine's are not suitable for micro-bore systems, Co I got mine from dont recomend P/F micro bore , what size pipes have you got from boiler ? sounds like problem on return pipes, poss blockage around manafold, you can clean out these systems but it takes quite some time, have you got an inline filter close to boiler ? may be good idea to fit one.