Boiler Change Advice

[FozzieBear]

I am looking for advice on choosing a replacement boiler for my bungalow. Firstly a bit of info.
The building to be heated is a large 4 bedroom bungalow with a garden room and study. The building is well insulated and has underfloor heating throughout, with a towel rail in the bathroom and en-suite to act as a bypass. The system is open vented with CW storage and expansion tanks and hot water cylinder and is fully pumped with two control valves. The underfloor heating (Wirsbo) was laid by myself when rebuilding the bungalow, but has been extended to cover the garden room and new study. There are two area packs each with their own pump, one which services the heating for the bedrooms and the second the main living accommodation and study and garden room.
The existing boiler is a Potterton Profile 60e, which has been in service for nearly 18yrs. I have only had to change the ignition circuit board and service the fan in that time but the flue gases is stripping the paint off the external render and the fan is starting to whine again, so I thinks its time to get a new boiler.
I have clearly got to get a condensing boiler, but as everything else is sound did not see the point of a combi. I have read a lot of reviews about the Valliant Ecotec which appears to have a stainless steel heat exchanger and good performance. However looking at the Valliant website, all the boilers appear to have bottom connections, whereas the potterton has two top connections. There is very little space either side of the existing boiler which is in an externally ventilated cupboard, and I cant see from the diagrams if you can run pipework inside the boiler or behind it to resite the flow and return to the top.

Firstly can you stand the boiler off the wall to run pipework behind, or will I have to look for another make of boiler with top connections.

Secondly I belive to run at its most efficient the return temperature has to be very low. Is this achievable with underfloor heating which already runs at lower temperatures?
Finally if the Ecotec is a goer, is the VRC430 worth spending the extra on underfloor heating is slow to respond to rapid changes in outside temperature?
Fozzie

 

[linkyplumb]

the 400 series Vaillant, is an open vent boiler, and has top connections.
If going down the vaillant route, then I would advise to get all vaillant controls, as they work well together.

 

[ALEC1]

the major barrier to getting low return temperatures is moxing valves on you current system, which require a flow temp up to 75c to work correctly.

ufh is perfect for weather compensation precisely because it responds to outside temperature before the heat has left the house...

i woul be buying a system boiler such as the 600 series vaillants or the viessman vitodens 200s with weather comp..and removing the mixing valve and manifold pumps...

 

[ALEC1]

vaillant do have a stand off kit...

 

[FozzieBear]

Thanks LinkyPlumb I must have been looking at the combi systems not the heat only bolers. I finally managed to download an installation manual which shows just as you said, top connections

Fozzie

 

[FozzieBear]

the major barrier to getting low return temperatures is moxing valves on you current system, which require a flow temp up to 75c to work correctly.

ufh is perfect for weather compensation precisely because it responds to outside temperature before the heat has left the house...

i woul be buying a system boiler such as the 600 series vaillants or the viessman vitodens 200s with weather comp..and removing the mixing valve and manifold pumps...

Thanks Alec 1
To clarify, you are suggesting removing the existing thermostatic mixing valves and circulating pumps on the two UFH zone packs? If so how do your regulate the flow temperature from the boiler to the required low temperature used by the heating loops and what safeguards are there to avoid over temperature and damaging the pipework?
Also what about DHW and running the boiler at a high enough output to maintain the hot water at a reasonable temperature? The only way I can see to achieve this is a single thermostatic control on the flow to the UFH zone packs, with the DHW taken off before this? Unless this negates removing the mixing valves?
Finally will a single circulating pump with a head of say 8m be sufficient to push water around all these circuits. At the moment there are three pumps doing the job!
Fozzie