Do I need to upgrade my pipes as well as my pump?

[david2012]

My domestic central heating system is configured (very simply) thus :

two Potterton Suprima 120L boilers connected to the same cold input and common hot output
Grundfos UPS 15-60 pump
20 radiators
pressurised system with TRV on 18 radiators

It's a 5 bedroom house, the boilers were put in 12 years or so ago by the previous owners.

We moved in a few months ago and one of the boilers (to be known as 'the left boiler') regularly trips out, the red light flashes and the green light goes out. According to the manual this is due to a dud thermostat or overheating.

British Gas came round to check over the system as part of the annual service and I pointed out the problem with the left boiler. After taking a look the engineer told me that the problem was overheating and that the pump was not up to the job. He also said that these boilers are recommended to be installed with 35mm pipework rather than the 28mm that has been used. He recommended a pump upgrade and a pipework upgrade. The recommended replacement pump is a Grundfos UPS 25/55

So now I have a list of questions...
is this the right pump? Grundfos say it is obsolete and that the MAGNA1 25-40 is compatible
is it essential to have the pipework upgraded or would the new pump be OK with the narrower bore?
is this simple enough for DIY? I'm fairly competent with DIY and have done a bit of plumbing (compression joints generally )
are there any other suggestions? Someone I know suggested a second pump in series with the first
what else am I missing?

The quotes have come in and now I know how BG make there money! Manpower is 88ph and the pump is available online for almost 1/2 of what BG want to charge!

Excuse my vagueness, if there is anything obviously missing please tell me.

Thanks!
Dave

 

[hazetimesfive]

i wrote a lot then i deleted it

 

[mogget]

I'm no expert on systems like this but I do wonder how equal flow between the boilers is achieved on only one pump.

And that's some heat output! Do you really need 70kw in a 5 bedroom house with 20 rads - how massive is your house ?!?

Wow!

 

[david2012]

I'm no expert on systems like this but I do wonder how equal flow between the boilers is achieved on only one pump.

And that's some heat output! Do you really need 70kw in a 5 bedroom house with 20 rads - how massive is your house ?!?

Wow!

Well to be honest I wonder if two boilers is overkill, he heating is running on just one and things feel fine but the furthest rad is not very hot. I don't know if this means that the good boiler (the right hand one) is working overtime but at the mo' it seems happy enough. Don't know about when it gets really cold outside though.

 

[JBPHS]

You desperately need an engineer who has experience in coupling 2 or more heat sources to a system correctly. Usually someone who has some experience in commercial work (preferably in plant rooms). Continue like this and/or attempt to do it all yourself, then run the risk of future overheating problems, etc.

James

 

[Dan Robinson]

2 120's?


Nuts.


Don't think you need a Commercial guy - just some one with half a brain .

 

[mogget]

Approximate your radiator outputs using the Stelrad Elite catalogue

http://ukweb.stelrad.com/uk/resources/files/b9f4facf41064b974ee7dc716fd5ca26/elite.pdf

Add them up, add 2kw for each hot water cylinder, and I bet it doesn't add up to 70kW!

Delta T is the temperature difference between radiator and air, so (for the sake of argument) if you run your rads at 70degC use a delta T of 50degC.

Then you might get some kind of answer!

 

[hazetimesfive]

Delta T 50

 

[mogget]

I did say for the sake of argument, I guess.

 

[Dean744PiN5]

Thats gonna cause a bit of thermal shock

 

[JBPHS]

2 120's?


Nuts.


Don't think you need a Commercial guy - just some one with half a brain .

Could be sized correctly for Downton Abbey!

James

 

[mogget]

Have I made another scatterbrained f*ck-up?

70deg (rad temperature) - 20deg (air temperature in room) = 50.

 

[hazetimesfive]

Delta T 20

 

[Dan Robinson]

Place were specing for is not far off Downton Abbey -that only has 80kW of oil boiler which has to do the swimming pool as well .

Well - I say like Downton Abbey - I haven't watched it. This place has 29 acres of woodland though.

 

[mogget]

Delta T 20

Ok I am missing something here, which delta T are you talking about... please educate LOL.

Delta T flow / return?

Delta T average rad temp / air temp?

Delta T room temp / outside temp?

As far as I understand it, Delta T is just a difference of temperature and can apply between any two given temperatures.