Boiler for a larger house

[dybleah]

Hi all, asking for some advice after reading around a bit please

My parents have a 5 bedroom (2900 sq ft) house with 3 bathrooms. The boiler is in the original part of the house (so it is situated on one side of the house). We found several problems with the system over the years. They built a significant extension years ago and the radiators there don't heat up very well (maybe narrow pipes or not powerful enough system/pump/flow). There is very low flow (cold water 3L/min and hot 7L/min) of water in the house. I think they have called the water suppliers to try to increase this, but I also suspect that the old piping system is narrow gauge (not sure exactly what diameter). The other issue is that the immersion heater is broken and the only way to access hot water is to switch on central heating (which I don't really understand).

The heating system is an old >15 year old British Gas 330 boiler with a 140 L tank + 2.8kw immersion heater. There is a water tank in the loft.
We installed a water pump for one of the toilets and it whirrs away when hot water tap is switched on
There is another pump (not sure when it was installed) - Grundfos ups3 15-50/65 130 - in the boiler cupboard
There seems to be a huge complexity of pipes (as seen in the photo)

I'm looking to simplify the system and wondering if a combi boiler is the way to go. We don't use more than 2 hot water sources at a time. I understand that the central heating will be fine with even a reasonably low Kw rating and that hot water on-demand is the key factor to consider. After reading around, it seems like my pumps are inadequate and my water flow is too low to begin with.

With this background, is there even a point in 'upgrading' to a combi boiler with a higher Kw/flow rating (£3.5-4.5k)?
It feels outdated to have a water tank/immersion heater/ insulated tank setup, but I'm no professional!

Thanks for any advice everyone!

 

[Madrab]

5 Bedroom and 3 bathrooms - a combi would not be recommended in that size of house. A combi really can't deal with more than one outlet at one time without a major impact to output. Even a high output combi can struggle depending on the cold mains supply and what the outlet outputs are.

The 330 is a rebadged Glowworm Flexicom - a basic budget box, if it is performing correctly, is nice and clean and tidy and has been serviced etc then no real need to replace.

An open vented system isn't outdated, it is old and trusted tech. A whole house pump placed at the bottom of the cylinder could deal with the hot water delivery issue. Cold water requires a better look and a better idea of what the mains can deliver (dynamic flow and pressure) and what the distribution pipework within the house is like. If the mains can support it then an unvented HW system may be a solution.

Central Heating requirements - basic check - size up all the radiators as far as their output is concerned and see what the total output is. If the current boiler has a 30Kw input then it suggests, if it has been sized correctly, that there is a significant radiator load.

You really need an experienced pro in to perform a whole house survey. Only so much can be suggested though an online forum.

 

[dybleah]

Thanks, and will definitely get a pro in to look. But just in the meantime, I wanted to be more informed about the issues and options in the house.

Currently the flow is slow for both hot and (especially) cold water. So I think even a bigger powered boiler wouldn't be useful. If a combi boiler is not a good choice, then is there a way to minimise the costs of having an open vented system with boiler/tank/further tank in loft? My immersion heater in the tank next to the boiler is 2800W! This would be on for a lot of the day (esp in winter). This is hugely expensive!

The Grundfos pump has no sound coming from it when the water runs. Whereas the other pump installed does have a whirring sound when the nearby toilet is flushed, for example. Is this normal?

What is the best option for poor flow in the taps despite 2 pumps!? Central heating is generally ok in the main part of the house and radiators warm up quickly. The extension is another issue...radiators always stay lukewarm. Maybe it's the piping issue there.

Thanks again everyone

 

[Madrab]

The cold flow problem will be down to those cold outlets being fed from the large cistern in the attic, there should be one tap, usually the kitchen tap, that is mains connected and that would usually have a higher output.

The Grundfos pump is for the central heating, not for the hot or cold water supply.

Not sure what you mean by minimising the costs with an open vent system? Running costs really isn't a factor, against an alternative sealed system.

The HW cylinder would always be heated by the central heating, it's much more cost effective than using the electric immersion element, the immersion heater is only there as a backup if the CH fails. The CH should be timed to heat the HW cylinder at certain times of the day and would be set by usage.

The extensions radiators need to be balanced.

 

[ericmark]

My son went from a twin boiler system one for DHW and one for CH to a single combi boiler and from an open vented to pressured system, the only change was all the radiator valves started to leak.

In real terms CH does not need much flow, we restrict the flow at every radiator using the lock shield valve to a rate the TRV can handle, if flow is too high, we get a hysteresis as the TRV can't open or close fast enough.

It's not easy in a large house, I am still trying to trim in this house, 5 bedrooms, 3 bathrooms, 2 kitchens etc. over three floors, I have fitted zone valves so I can turn off lower floor, upper two floors have 9 programmable TRV heads.

With the upper floor I can set a sequence, so when the CH starts it does important rooms first, however since the oil boiler does not modulate, to stop is cycling really want to use the full 20 kW when reheating.

But I know what my problem is, it is all down to the location of the wall thermostat, however two things, one crossing fingers and hoping Nest release the temperature sensors in the UK, and two new patio doors will likely change how the rooms retain their heat, so fastest cooling room could change.

I can control how fast a room heats, but not how fast it cools, and with a single wall thermostat it needs to be in the room which cools the fastest. I would have expected the hall, but no, that's the slowest room to cool.

All other rooms are not used 24/7, so are not heated 24/7, so only other option is a mobile thermostat, so think this year will get a cradle for the thermostat and try moving it room to room. Either that or abandon Nest Gen 3 and use some thing like Drayton Wiser, Honeywell Evohome, or Hive, i.e. one where the TRV's talk to the hub, however since already using programmable TRV heads, it seems a huge expense with very little gain.

Like many people the CH control has grown, but not in a structured way, I arrived in the house with 4 Energenie Mihome TRV heads from late mothers house, where to be fair they had worked A1 without having a linked wall thermostat. It was claimed Nest worked with them, so when I realised this CH system was in a mess, and I needed a method to control a boiler on the lower floor from middle floor and I had only 2 wires, Nest Gen 3 seemed to fit the bill.

However the link wall thermostat to TRV works wrong way around, the TRV's follow Nest, not Nest following the TRV, and although using the app to change temperature setting it worked, using a set sequence or turning dial did not, so just set the two with same program, they are not linked any more.

But sons house (my old one) and mothers house, worked fine with one wall thermostat, it is all down to house design, and how the house catches the sun, and cools. So I fell into the time old pit fall, it worked with that house so it should work with mine, and I was wrong.

So you need to look at the home and try to work out what is going on. Is a wall thermostat turning off too soon, are the lock shield valves set A1, are the TRV's set correctly, the *123456 on a TRV is rather hard to work out, I have one in my desk draw, replaced soon after moving in, and set at around 2.5, it starts closing at around 18ºC but is not fully closed until around 22ºC which can be an advantage, as a wall thermostat in the same room set to 20ºC will work 19.5ºC on and 20.5ºC off so between the two they can control the CH well. But I prefer a TRV which says 20ºC, makes life so much easier.