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Old boiler less than effective, 20 years old, makes some worrying gurgling noises when running the central heating so time for a change.
It's an old style big hot water tank, cold tank in the loft and tank for the central heating in the loft too type of thing.
Some of the central heating appears to be working on a single pipe routed through the radiator basis, other rads take a 'spur' off a two pipe system.
It's a fairly large house with two bathrooms so moving to a mains pressure hot water system with a tank seems the best route (rather than combi boiler)?
Questions;
1) how much of the existing hot water system do we need to replace to switch to mains pressure? There's a pump for the upstairs shower currently (Shower is nearly level with the cold tank in one of the lofts).
2) do we need to replace the central heating pipework or can we just connect a new boiler up to existing?
The house is 600 years old and some of the routing of services is, errm, interesting so I'd like to disturb as little as possible of the existing pipework.
Unfortunately the answer to both questions is "it depends". You say two bathrooms, do you mean two showers running simultaneously? Then I reckon you'd want an unvented system based on the unpleasant personal experience of living in a house with a combi where two people taking a shower resulted in a water flow equivalent to an elderly bloke with prostate problems.
You wouldn't need your shower pump any more provided your mains water pressure is sufficient.
Don't know about replacing pipework. Personally once the level of disruption for the install reaches a certain point I'd be replacing radiators and pipework (you don't need to follow the same route as the original pipes).
Old boilers are usually pretty robust - not quite as efficient as the current crop but cast iron heat exchangers etc seem to last forever. Does it definitely need changing?
Flaperon
Old boilers are usually pretty robust – not quite as efficient as the current crop but cast iron heat exchangers etc seem to last forever. Does it definitely need changing?
That's a good point, the new ones seem quite fragile and you can easily wipe any efficiency savings out with a repair or two. We had a diverter valve, heat exchanger and something i've forgotten replaced under the extended warranty on ours. The bill would have been hundreds. Think the heat exchanger alone is something like £200.
"Then I reckon you’d want an unvented system based on the unpleasant personal experience of living in a house with a combi"
Yes, that's what we're considering - unvented but not combi, the second bathroom is currently electric shower but we want to convert to be fed from hot water system
Problem is the house has solid walls with a lot of wooden paneling and I'm loathe to start pulling random panels off walls to access pipework if we can avoid it - I think the making good would cost as much as the boiler. Most of the rads are the old style ones which suit the house so we'd want to keep and they cost a lot new.
I think the boiler is probably past a refurb in terms of age and a like for like replacement keeping the vented system seems like an opportunity lost if we can manage to switch to a more modern approach.
Unvented cylinder manufacturer here.....If your original vented system was installed at the same time as the 'one pipe' radiator system, then its quite old.
your pipework pressure is likely to rise from 0-0.6bar at the moment up to 3barish depending on your mains water pressure. its entirely possible that you will find out exactly where the weak points in your pipework/fittings are when you turn the water on pst-installation.
this happens quote a lot and unless you are prepared to upgrade the pipework in advance, theres not much you can do other than go for it.
before you do make the call, get a check on your mains pressure AND flow rate at various times of day - pressure is ususually highest in the morning and can drop off during the day depending on how good the mains system is beyond your property boundary. check the spec on the showers to see that they can work on the mains pressure you can get - seen a few high end showers that need a minimum 3bar.
Be aware that the discharge pipe from the new unvented cylinder has to follow certain rules (constant fall, terminate externally, max length/number of bends) that may be tricky in a 600yr old house. ensure your installer has the G3 ticket for unvented.
HTH
I'm not a plumber.
I don't think the radiator circuit is related to the hot water one. We put an unvented hot water cylinder in our old house, replacing a header tank and cylinder like you're considering. Still needed to top up the water pressure in the central heating system from time-to-time by opening a valve - which leads me to think that it's on a different circuit. In which case the only pipes you'd need to worry about handling mains pressure are the hot water ones. I.e....
1) how much of the existing hot water system do we need to replace to switch to mains pressure?
No idea. (We didn't replace any of ours, but our house was only 90 years old, and the mains pressure wasn't particularly high.)
2) do we need to replace the central heating pipework or can we just connect a new boiler up to existing?
Just connect up the new boiler.
I’m sure the more knowledgable will correct me if I’m wrong (iamnap) but you can split this up by replacing your system boiler now if it really requires it, and choose to convert the system to unvented at a later date. Presumably you also retain the option to keep the heating with vented and at low pressure, but swap the cylinder for an unvented to give you mains pressure Domestic Hot Water. Remember that the DHW and CH circuits are seperate systems that are linked.
We run two showers (and the rest of the house) off a combi boiler without any bother. Isn't it just about the size of the boiler?
@golfish24
That's exactly what I have done.
I'll also second the higher pressure will find leaks etc! I slowly increased pressure and some didn't turn up until nearly 3 bar! Lots of swearing as I drain the system for what feels like the 34th time.
It sounds like you CH circuit could do with some modifications but it really requires a plumber to trace it all out and work out what the options are. It may be you can get away with a few small changes and some zoning.
do we need to replace the central heating pipework or can we just connect a new boiler up to existing?
We had the same set up when we moved in but the boiler part was in the kitchen and huge, as part of the getting our kitchen done got a combi installed and had it moved to the loft, only pipe work done was to join it up to what was already in the house. house was built in the 80's though. ty
We run two showers (and the rest of the house) off a combi boiler without any bother. Isn’t it just about the size of the boiler?
Agreed. We have a new system in and uprated the combi to allow for this. We have two bathrooms and three en-suites but one of those is electric shower (good to have as redundancy) and we figured it is unlikely to ever have more than two of the other showers running at once.
Have a look at Harlequin HeatStream. It's a vented hot water store that heat exchanges into a main pressure dhw system. It's what I'll be going for as recommended by a plumber I know who's installed a fir few instead of unvented systems.
It's a bit of a hybrid system and has some different pros / cons to the other systems.
You can also get combis with build in pressurised storage but it can all be sized to suit demand.
Sounds like a thermal store, or thermal store plus plate heat exchanger.
IIRC you cannot legally pump water on a mains-fed system (from conversations I had with our plumber seven years ago) as you are not permitted to pump water from a general supply (it’s fine to pump it from a traditional header tank /boiler set up as you are pumping from your store). Although I might be misremembering this - is it combi boilers you can’t pump from?