Dodgy Boiler Installation - More advice requested please!

[Barbusa]

I posted a message back on 12th January regarding a dodgy boiler installation and received from really useful advice.

Basically, the story is that about one year ago I had my old Myson combination boiler replaced with a new Potterton Performa 24 and the installing engineer, using the existing pipework, connected it in the same way as the Myson.

The problem was that the Myson, a Midas Sfi had the central heating return on the left and the central heating flow on the right whereas on the new Potterton Performa 24 they are the other way round.

The engineer, for some reason, did not take this into consideration and, because of this, has connected them the wrong way round, which explains all the problems we have been experiecing with radiators and pipes 'whirring' and then banging.

Because we do not have a roomstat or a radiator with lockshields fitted the advice I was given via this Forum was:-

The installation did not conform to Building Regs (2002).

To put things right the following works needed to be carried out:-

A/ alter the pipework under the boiler so trv are on the flow
B/ remove a trv and replace with lockshield
C/ fit a rf roomstat in the coolest part of the house[hallway]and make the hall radiator a bypass with a pair of lockshields[interlock]

I pointed this out to the Firm that installed it and yesterday they came round to put things right.

To my complete surprise, all they did was to change the existing TRVs so that they now are fixed horizontal to the vertical 'return' pipe coming up through the floorboards, instead of vertical, as they were.

As before, all seven radiators (three floors), are fitted with TRVs.

The senior of the two engineers that came told me this would solve all our problems.

He also told me:-

"The makers of this particular boiler recommend that the TRVs are fitted to the return as it is cooler than the flow so the engineer who installed it did so correctly.

The Building Regulations are purely 'best practice guidelines' and not in any way compulsory so we do not need fit a roomstat or lockshields. The only time that you may be asked about this is if you were selling the property and if this was the case you will just have to make sure that any prospective buyer was made fully aware of this.

The boiler has an internal bypass so there is no need for lockshields to be fitted and a roomstat is also not needed as the TRVs will do the same job"

-----------------------------------------------------------------------------------

I was a little suspicious of this and have contacted Baxi Potterton, the manufacturers of the new boiler, by E-mail and, although very reluctant to give any information, in writing, suggesting instead that I telephone their Customer Helpline, they did say the following:-

"Following your enquiry regarding the Potterton Performa, no such
recommendation from ourselves, usually TRV's are on flow. If you require
any further information please don't hesitate to contact the technical help
line.

I would be very grateful for any further advice on this one.

 

[Bahco]

The boiler has an internal bypass so lockshields are not required.

Most TRVs are bi directional so if they are not 'chattering' do not worry.

You should have a roomstat though to conform with Part L and lockshields on the rad in the same room as the stat.

 

[Barbusa]

Thanks for that, however I don't think our TRVs are 'bi-directional' because, originally, to cure the noises and banging, they were goingto quote us a fee for changing all the TRVs to 'Dual-flow' ones which they estimated would involve a day's labour!

 

[brentwood]

'Building Regs are just guidelines'. Time to give your local Building Control Officer a ring! If the installer wasn't 'Self Certifying' then you'd (in theory) have to have notify Building Control yourself. Man's either ignorant or lying.

 

[ricarbo]

It doesn't matter if the TRV's are on flow or return as long as the flow is in the right direction. The convention is to put them on the flow, but it's just that, I believe.
You are supposed to use a room stat, to prevent the boiler firing when the house is warm enough. your boiler has a switch in it which prevents firing for 2 minutes if there's no flow, when it tries again. But the regs say you should have a wallstat.

 

[Agile]

I would not have been happy with that solution!

However, TRVs actually work better on the return because they pick up less heat from the pipes.***

TRVs also work much better when the sensor is horizontal for the same reason.

My reason for not wanting them to be fitted horizontally is that they are much more liable to accidental damage from vaccuum cleaners etc. which outweighs their operating advantage for me.

The internal by-pass in the boiler is solely to protect the boiler and an external one should be fitted and now MUST be fitter. Likewise the room stat MUST be fitted as an interlock ( unless the boiler has a suitable interlock ). Some people still have not done the Energy Efficiency course.

Tony Glazier

*** TRVs were traditionally fitted on the flow because thats the way they were designed for the single flow direction when fitted vertically.

 

[Bahco]

The internal by-pass in the boiler is solely to protect the boiler and an external one should be fitted.

Can you explain that statement please Tony?

We were taught at college that bypasses are no longer reqd with an internal boiler bypass. Surely this will be enough to protect the boiler.

 

[Agile]

I must assume that you have not done the energy efficiency course yet ( or have forgotten some of it ).

As you say the internal by-pass is adequate to protect boiler.

However, the energy efficiency regulations require an auto bypass to be fitted, since April 2005 I think, probably as part of the condensing boiler package.

I dont write them! I dont necessarily agree with them either but we are expected to follow them.

As far as I can guess the idea is to allow ALL rads to have TRVs and save the energy that could be wasted by a rad in the bathroom without one.

Tony

 

[ricarbo]

Agile wrote
( unless the boiler has a suitable interlock ).
In the case of this boiler, which detects absence of flow, this is an acceptable substitute for a wall stat, isn't it? I would agree it isn't 'best practice' though, because that expects a programmable roomstat, permitting different temperatures at different times of day.
Why should the bypass be external to a boiler with an integral pump? What's the merit of two bypasses?

 

[DP]

If you look at some of the MIs, they will tell you an internal bypass is incorporated within the boiler. It will also tell you an external bypass must be fitted. This was the case with most Vokera boilers (when I use to fit them- now no longer fit boilers- only repair them)

Vaillant VCW 242/ 282 type was the exception. It had an internal bypass and did not require an external one.

 

[Paul Barker]

What I recall of my energy efficiency course about roomstat was

Must use rstat minimum practice
Rstat zone must not have a trv, so how can you talk about every rad having a trv.

Therefore how come you need a bipass?

IF you use a bipass it must be an auto bipass, but you doi not HAVE to fit a bipass unless MI's specifically state so.

With regard to manufacturers, my main boiler the Buderus, I asked the BBT engineer and he said no need for bipass the way I install them.

Where has all this about bipasses on a correctly designed system come from?

Have I got this wrong? Di I have to now buy an auto bipass for each installation now, as well as all the other stuff we're doing that the last generation of heating engineers didn't lift a finger towards?

 

[Agile]

I have just had a look at the MI for this boiler which is stated to be a Performa 24.

It states there is an integral bypass and does not say there is a need for an external bypass. ( It does not say there is not a need for one either. )

The energy efficiency regulations say that an auto by pass is required to be fitted. We could qualify that to mean that when a bypass is required by the MI then it has to be an AUTO type and a lockshield valve must not be used in place of a bypass.

We could assume the manufacturers dont think one is essential. However it may still be useful to have one if the TRVs are likely to become noisy as they are closing and the pump pressure becomes higher.

In spite of what Ricarbo suggests above I could find no mention in the MI of an interlock within this boiler and it says the pump closes down after 30 sec. I therefore conclude that a room stat IS required to meet the regulations.

As Paul says a TRV should not be fitted in the room where a room stat is located. However, that rad cannot be used instead of an auto bypass ( when required ) because the user could turn that rad off.

Tony[/u]

 

[croydoncorgi]

I really don't care about the GENERAL advice about bypasses (or not) offered on E/E courses. GENERALLY, an auto-bypass is a 'good thing'.

BUT the key to energy-efficient operation of a condensing boiler is keeping the Return temperature as LOW as possible. If the hydraulic design of a system is such that the bypass opens when the burner is on (because the resistance of the whole system is too great) then it is a bad design! The water flowing through the bypass in this situation will obviously be hotter than water that has been through a radiator, hence will raise Return temperature - which will potentially inhibit condensation!

The auto-bypass should ONLY operate when the burner is OFF and the pump is over-running. So I cannot see any actual reason why an integral bypass (if fitted) should not be completely sufficient, with no need for another, external one.

 

[Paul Barker]

On the Baxi combi training the guy said that they had to fit bipasses inside the boiler to protect it because folk weren't puting them in the installations.

I think I'll start using autobipasses just to be safe, I suppose the ideal place is on the drops for the one rad controlled by r'stat, so that should an ignorant user shut that rad valve the auto bipass is there to protect the pump/boiler.

WHat's needed is an auto anti ignoramous device that hits them over the back of the head with a lump hammer when they do something stupid.

 

[Agile]

Its generally recommended that the auto bypass is fitted immediately after the boiler to reduce the length of heated pipe if all the rads are off.

Tony