Central Heating Plumbing Question

[Sqwimbob]

So we bought an old house, it's an odd shape (10 external walls versus your usual 4) due to various extensions. Since we moved in the central heating has been a bit of a mystery in terms of pipe routing, though I should have guessed it would be 'interesting' based on the fact that more radiators run of the HW circuit (7) than the CH circuit (4).

Having spent a couple of weekends lifting floorboards to ascertain exactly what the layout is I have put together this schematic diagram which details (as best as my limited Visio skills are able) the bananas layout that looks like it was designed by a blind monkey:

Longer term there will be UFH, a heat pump and quite probably a major replumbing. In the short term I need to get rid of the red pipe, it's an old ~1.5" steel pipe that runs under a suspended ground floor that I am insulating beneath and which I'd rather never have to disturb again.

My questions, which I'd appreciate thoughts and opinions on:

1) Can I replace the red pipe with the proposed green pipe?
I understand that best practice is that the HW cylinder return should connect directly (be the last connection on the return) to the boiler, but there are already three radiators plumbed like that and the system is still keeping us reasonably warm when it gets cold. Will one more really be the straw that breaks the camel's back?

2) Unrelated to #1, if you were insulating between the joists of a suspended ground floor room and had the chance (as currently have access), would you
a) run well insulated pipes under the floorboards to the radiator in that room where it will be sealed away out of sight, you'd be hard pushed to ever know if it was leaking and a pain to get to if needed in the future (though you'd hope that would be an unlikely requirement)
or
b) run pipes to the radiator around two walls of the room behind the skirting board

Thanks
Sqwimbob

 

[endecotp]

So the feed and expansion pipes are both on the far side of the 3-way valve?

 

[Sqwimbob]

Ah, good spot, thank you. My diagram was not quite correct - I have edited and corrected. The F+E tank is plumbed as per the updated diagram. So yes plumbed to the far side of the 3-port valve, with either the valve or a radiator between it and the boiler.

 

[endecotp]

So if the boiler is heating the HW cylinder and a few radiators are turned off, there is no path from the boiler to the expansion pipe? That’s dangerous. I think there should be a direct, 22mm pipe from the boiler to the expansion vent. (Experts, am I right?

 

[Gasguru]

You've got the heating equivalent of the internet with so many routes the water can flow.
Just rip it all out and lash it back up to get a basic system running.
What boiler model?

 

[fixitflav]

Having spent a couple of weekends lifting floorboards to ascertain exactly what the layout is I have put together this schematic diagram which details (as best as my limited Visio skills are able) the bananas layout that looks like it was designed by a blind monkey:

Couple of quick ones
Where is the pump?
As shown, the system doesn't meet the rule - all rads returns must be commoned before the HW cylinder return joins

 

[Sqwimbob]

Thanks for the responses.

Boiler is a Glow-worm Ultimate (80FF) boiler of unknown (but certainly getting on a bit) vintage.

The pump is on the flow side of the boiler, next to it.

 

[fixitflav]

So if the boiler is heating the HW cylinder and a few radiators are turned off, there is no path from the boiler to the expansion pipe? That’s dangerous. I think there should be a direct, 22mm pipe from the boiler to the expansion vent. (Experts, am I right?

I wouldn't claim to be an expert, but the way I see it is Chloe's rad must be open to allow expansion when in HW mode (so the CH port in the 3-way is closed). Release of any air/gas is another matter.

 

[fixitflav]

Can I replace the red pipe with the proposed green pipe?

I don't suppose it would be any worse than it is now. I can't imagine what dark night of the soul the guy who installed that was going through!

I understand that best practice is that the HW cylinder return should connect directly (be the last connection on the return) to the boiler, but there are already three radiators plumbed like that and the system is still keeping us reasonably warm when it gets cold.

The issue isn't that the rads won't get hot, it's that in HW mode there is a flow through (some of) the rads, wasting gas, and in summer possibly overheating the house

 

[Sqwimbob]

Thanks all. Some good info to go on. Absolutely agree it's not how any same person would design a system.
I guess since all but towel radiators in bathrooms have TRVs then there isn't much flow up the pipes to the radiators from the main spine - we haven't noticed those radiators getting warm when just the HW is on during the summer months.

 

[ericmark]

I looked for your pump in your plan, and can't see it. My central heating had also been extended, and it used two pumps, it seems likely the person doing it, thought they could select main house or flat by selecting the pump in use, this did not work, using one pump resulted in reverse flow in the other pump, so I had motorised valves fitted.

The DHW was thermo-syphon, with no thermostat, and the timer had a 1.5 hour minium on time, changed for one with ½ minium on time (Nest Gen 3) and experiment showed ½ hour 4 times a week was not quite enough, and I was worried about legionnaires, but to get cables to the tank would be a major task.

So when we got solar panels, I also got an iboost+ to heat the DHW with spare solar, hindsight it was a mistake, but it shows me how much energy saved as it puts it, it to begin with was not that good, the immersion heater was too short, 9" and was using around 5 kWh per week, got it swapped for a 27" immersion heater, now using around 15 kWh per week, and we have far more and hotter DHW then with the boiler running for 2 hours in the summer, not a modulating boiler, so since it is 20 kW, we were using 40 kWh per week.

Looking at how much oil used, I think we were using more than 40 kWh per week, but we have realised it is actually cheaper to use the immersion heater in summer to the central heating boiler, this will clearly vary home to home, but the energy required to heat the boiler and pipework, when it only ran for ½ hour, was a lot higher than we had thought. So you also may find in summer, using an immersion heater works out cheaper.

 

[fixitflav]

I looked for your pump in your plan, and can't see it.

See #7

 

[ericmark]

See #7

Missed that, I do look at it and think that looks like a lot of pipe work boiler to hot coil, if it is a hot coil, and I found with mine the losses are really too high to be worth using the boiler in summer.

Losses from pipe work in winter is not really a loss, as it still goes into the home.

I have looked at my own, and I realise there are many improvements which could be made, however the question is if worth it? If it isn't broke, done fix it. The red to green does not seem a problem, but the comment "I'd rather never have to disturb again." and "Longer term there will be UFH, a heat pump and quite probably a major replumbing." don't seem to belong together.

There seems to be two schools of thought with central heating.
1) Heat whole house 24/7.
2) Heat only areas required as required.
The second looks for fast response times, the first does not, and UFH does not respond fast. Sometimes the sun through windows means we also need fast response times.

To design central heating is complex, and I have in the past got it wrong, things which until it happened never entered my head, like how fast the sun in a bay window can heat a room. And a plan of pipework will not help with that. I had also not realised how much until the central heating fires up, the temperature can vary within one room, and how a TRV on a radiator next to a wall can be much colder to the room in general, so having the TRV fire up a boiler is not always a good idea.

I have made a lot of mistakes, but I am not a heating and ventilation engineer, one assumes engineer means over level 3 trained i.e. university, and I did not get my degree in heating and ventilation, hence a load of errors. So is it worth doing anything if all going to be changed again.

Personally, I want a warm house even if there is a power cut, so I have solar power, inverter, and battery which will keep my oil fired boiler running for quite a time after a power cut, I lived through the Winter of discontent, and so would never rely on grid electric, so an electric only powered heat pump is a non-starter. No reason for not having an oil fired heat pump, I suppose easiest way is having a generator, but that makes the whole thing rather expensive.