twin boilers, massive daily gas usage fluctuations and noisy recirculating pump

[Didi]

hello, we have just moved into a house which seems to have some problems: it has twin potterton suprima 80 boilers separated into 2 zones/2 thermastats supplying a total of 26 rads. The majority of rads have trvs - not all are working. I have been monitory the gas usage daily and plotting what gas settings we have and there are times with no rhyme or reason the usage increases by over 65%.... there are 3 rads on the system - at different ends of the house that only operate when both boilers are working, otherwise, we have logged a pattern of which boiler works which rads, and it looks like the previous occupants separated it out to control the main section of the house then peripheral rooms. We set the hot water temp at 50 degrees and can't understand what might be causing these fluctuations. The boilers were set at max temp on both of them.

With the grundfos recirculating pump for the hot water, it sounds like a helicopter is in the building when it comes on and some of the taps take up to 2 mins for hot water to come through, not before cold water comes out that is absolutely freezing. These taps are in the centre, bedroom level, of the building and the ones furthest away are fine and quite quick, as is the kitchen tap which is on teh ground floor under the bathroom with the cold feed. The flow pipe seems to be 15mm on all connections from what we can see.

Any help on any of these would be greatly appreciated, as it is so unbeleivably costing to run teh gas, and I don't beleive that this is a true cost refelction as we set thermastats to 18/19 degrees.

thanks

 

[BBV]

Hmmm....as for your heating problems it doesn't sound like the boilers are working together as they should. Is there a low loss header fitted, (big tubular thing coupling the to boilers together?)

 

[Didi]

Hmmm....as for your heating problems it doesn't sound like the boilers are working together as they should. Is there a low loss header fitted, (big tubular thing coupling the to boilers together?)

Hi - just googled what they look like and hunter around the system and can't see one...

How should twin boilers operate as can't seem to find a straightforward explanation of how twin system should be set up?
thanks

 

[plumber0808]

Obviously you have a few problems. Get a qualified engineer to have a look and give you the correct guidance to go forward.

 

[BBV]

Hi, In my eyes it sounds like one boiler is laboring over the other, one is doing all the work when they should work together as one unit....irrespective of your two heating zones. I'm guessing one room stat does upstairs and the other down?

The reason one boiler is labouring over the other is probably because of something simply like flow and return pipes to boiler 1, tee off first or boiler one has better gas supply. The list can go one. I imagine one boiler has done majority of the work since they were fitted and maybe the previous owner didn't pay attention to it. The idea with the low loss header is to get an equal flow from each boiler. The flow should come down from each boiler then into a LLH so the water mixes together then goes off to different zones at the same flow rate and pressure.

Maybe someone ells can add to that, but I believe that is your problem. Hard to know without seeing it!

 

[SafeGasInstall]

You need a plumber to come over and work out the system operation ! He then could do anything you would like to have done !

 

[TBServices]

Sounds like the bronze pump needs replacing. Return from this should be sized down, so if you have a 22mm supply, the return will prob be 15mm after taps, if that makes sense. HW should be set to 65deg to prevent bacteria like legionnaires.

As for heating system, its impossible to say based on your description. I've seen houses that have 2 boilers running completely independently of each other to heat different zones, and systems where the load is shared. If your system is the latter, I would expect its not a very good install. Either way, it needs looking at by a reputable engineer.

 

[vern]

Have a good engineer look at this for you, it may cost just an hour for some good advice, and if your using gaslike you say a good survey will pay for its self, as gas is only going up in cost!

 

[Bronze_tap]

1.
The majority of rads have trvs - not all are working. ... rhyme or reason the usage increases by over 65%.... there are 3 rads on the system - at different ends of the house that only operate when both boilers are working,We set the hot water temp at 50 degrees and can't understand what might be causing these fluctuations.
The boilers were set at max temp on both of them.
2.
With the grundfos recirculating pump for the hot water, it sounds like a helicopter is in the building when it comes on and some of the taps take up to 2 mins for hot water to come through, not before cold water comes out that is absolutely freezing.

Any help on any of these would be greatly appreciated, as it is so unbeleivably costing to run teh gas, and I don't beleive that this is a true cost refelction as we set thermastats to 18/19 degrees.

thanks

I'm afraid your's CH/HW sys needs quite a bit of TLC... As it spends most gas heating the outer space, not the house...

1. Looks like the flow is a bit restricted, and I expect to find quite a serious deposits of the black gunk inside your's pipes/radiators.
So get someone skilled (preferably with FLIR camera), and have a look on the thermal properties of your's rads/pipes when running.
Also read: http://www.ukplumbersforums.co.uk/c...olution-how-do-proper-cheap-job-yourself.html
But for 28 rads I would take a week off + hire a good plumbing mate for that time too.
Also I would wait until the weather is a bit warmer. 🙂
It makes outside water work so much more pleasant... If your's mate have a powerflusher - than you can work inside, but make sure to invert each radiator with powerflusher connected directly to it + do the all feed/return pipes too ... (esp downstairs)

Try setting the boile's thermostats down, CH timers to always on, roomstats to 19 or so, and see how your usage goes... Also close cold air ingress points in the house, check insulation, leave the doors to staircase closed overningt, move one termostats to your's bedroom, upsize the rad there....

2. Get rid of the recircullator pump, and insulate/reroute the HW pipes. In some cases (20m+ HW run) POU (3-5L) water heater for the remote toilet sink may be more appropriate/economical.

PS: The hotter is your's HW tank, the faster it will scale up, the more water is wasted when trying to set the correct shower temperature, and the more heat it would dump in the airing cuppboard.
Legionella may be the problem if you've got 85 years+ old dudes AND unclorinated water supply contaminated with carbon source (nutrients for bacteria) sitting at 35 degrees for days.