To seal a central heating system or not?

[Jock Spanners]

Good morning everyone,

I have a big old vicarage which needs a new regular boiler. They also want fancy mixer taps in the kitchen . They have two hot water cylinders linked together, a shower pump and curved old radiators in the bay windows. I'm agonizing over what to do. The easiest option is to keep it gravity and simply change the boiler. The second option is to fit a large combi (there's only a short gas main). The third option is the unvented route. My worry is if I seal the system one of the rads will blow or a dodgy pipe joint will leak. I've risked it before and got away with it but I've known it go badly wrong for others. I don't want to suggest re-piping the house. What would you do?

Thanks,

Jock

 

[ShaunCorbs]

Plate the old system and seal the new boiler and maybe an unvented system if possible?

 

[Jock Spanners]

So you'd risk it?
I don't think they can afford to spend much more than the cost of a new boiler instal.

 

[SJB060685]

As shaun says put a plate in. Pressurise the new boiler loop and keep main system open vented. Will prevent any stress on the old system and also protect the boiler and its loop from corrosion etc.
Shaun and I know a number of people who love this idea 😂

 

[Jock Spanners]

This is new to me guys. How exactly do you do it?

 

[SJB060685]

Take your boiler primaries to a suitably sized plate heat exchanger and have the other plate heat exchanger ports to original system. You could pressurise the boiler and its primary loop to PHX and keep the original system open vented.

 

[EvilDrPorkChop]

Personally I’d just seal it and put a combi in. No issues with stored HW, if something does leak it’d probably would do eventually anyway even on OV. If system is big enough put a Low loss header in.
Just advise them accordingly before you seal it.

I may have misunderstood Vicarage - is it a place that's occupied or somewhere like a Church Hall? If it's a residence then Unvented and System boiler and seal it 👍

 

[Chuck]

If it's the big old system I'm imagining you probably want the plate HX in any event because it'll be difficult to impossible to flush the whole thing well enough to pass muster even if it is all leak tight. The cost of the plate will be offset by not having to spend a lot of time power flushing and in a longer life for the boiler.

If the boiler is in or close to the kitchen, it might be worth making it a combi having its DHW supply the kitchen tap with the HW storage tanks heated as a zone on CH circuit. This is worth considering if much water currently has to be wasted before the kitchen tap runs hot.

 

[Jock Spanners]

Take your boiler primaries to a suitably sized plate heat exchanger and have the other plate heat exchanger ports to original system. You could pressurise the boiler and its primary loop to PHX and keep the original system open vented.View attachment 44879

Thanks. Would I need a Pex designed especially for this? I can't picture how it's piped up. Does it have two pairs of ports? I assume this would also work with a system boiler?

 

[SJB060685]

Thanks. Would I need a Pex designed especially for this? I can't picture how it's piped up. Does it have two pairs of ports? I assume this would also work with a system boiler?

Sizing a PHX is not a straight forward process, lots of information is needed to calculate its size, a process im not too familiar with. Your best bet would be to speak to a heat exchanger company and supply them with some information they need. I know a number of people just go with bigger is better but it is quite a complicated process when sizing yourself.
As for tappings, it will be similar to a common PHX on a normal combi. It will have hot in and out and cold in and out.

 

[SimonG]

I wouldn't worry about it. Explain to customer potential issues. Cover it in your terms and conditions and let the customer decide.
Or price in a pressure test of original system.

Any work I do is covered by 'no guarantee on any existing pipe and fittings'.

 

[gmartine]

The plate is a good idea if they can find the money for it

Thanks. Would I need a Pex designed especially for this? I can't picture how it's piped up. Does it have two pairs of ports? I assume this would also work with a system boiler?

No something off the shelf, what size boiler?

 

[Jock Spanners]

I wouldn't worry about it. Explain to customer potential issues. Cover it in your terms and conditions and let the customer decide.
Or price in a pressure test of original system.

Any work I do is covered by 'no guarantee on any existing pipe and fittings'.

Good advice Simon. I'm minded towards this route.

 

[cricklewood]

Good advice Simon. I'm minded towards this route.

As a customer recently in a similar situation, I was reluctant to take a chance on a big expensive mess if pressurised old pipes gave way, so I went with another engineer who offered the PHE solution. Working well so far fingers crossed ...

 

[king of pipes]

The system is likely to be filthy dirty and very hard to clean I would leave it open how many kw is the existing boiler ? sealing it will be more costly it will need a decent sized expansion vessel a low loss header , extra pumps and zone valves , system protection is vital aswell Adey do a commercial type mag filter, any work that you carry out could cause leak issues please include I warning in your estimate and allow some wriggle room in that estimate for extra work if needed. Kop

 

[Nwalky]

Good morning everyone,

I have a big old vicarage which needs a new regular boiler. They also want fancy mixer taps in the kitchen . They have two hot water cylinders linked together, a shower pump and curved old radiators in the bay windows. I'm agonizing over what to do. The easiest option is to keep it gravity and simply change the boiler. The second option is to fit a large combi (there's only a short gas main). The third option is the unvented route. My worry is if I seal the system one of the rads will blow or a dodgy pipe joint will leak. I've risked it before and got away with it but I've known it go badly wrong for others. I don't want to suggest re-piping the house. What would you do?

Thanks,

Jock

If it were me, I would just put the ball in their court. I have had a conversion from gravity to sealed go badly in the past with radiators pin holing.

Go through with them about the benefits of a sealed system (I would probably go with the invented route rather than the combi) tell them of any problems that may occur and when you do the estimate put a note on it detailing the problems that may occur, such as leaking fittings, pin holed radiators etc and state that if any of this occurs then it will be an extra cost to rectify it.

I think the main thing is letting them know that you would like to better the system and make it more efficient by upgrading it but to also make them aware of every pro and con.

The last thing you want is for some mouth piece to come in after you have changed the boiler and ask why you never upgraded the system, at least this way they will be able to turn round to the person and say "well we were given the option but didn't want to risk the pipes not handling the pressure"

 

[Jock Spanners]

Thanks guys,
Long story short he's read an article in the Daily Torygraph about gas boilers being phased out by 2025 so he wants to explore different options. The journalist basically said that all we need to do is change gas boilers to air source heat pumps. If only!

 

[Pickwickpick]

Thanks guys,
Long story short he's read an article in the Daily Torygraph about gas boilers being phased out by 2025 so he wants to explore different options. The journalist basically said that all we need to do is change gas boilers to air source heat pumps. If only!

Sorry to hear that, the reporting on these things tends to be extremely poor. I really don't see why them being phased out in 5yrs (not convinced it will happen then either tbh) is a reason not to use them now, they will still be repairable with spare parts available and when it needs replacing in well over a decade things like air source heat pumps will no longer be novel and will be more cost effective.

 

[Chuck]

Sorry to hear that, the reporting on these things tends to be extremely poor. I really don't see why them being phased out in 5yrs (not convinced it will happen then either tbh) is a reason not to use them now, they will still be repairable with spare parts available and when it needs replacing in well over a decade things like air source heat pumps will no longer be novel and will be more cost effective.

AFAIK, the proposal is for no gas supply to new homes by 2025. Just another reason not to buy a new-build home as far as I'm concerned.

What will replace gas boilers in 2025? | Viessmann UK

Viessmann looks at the alternatives for homeowners following the announcement that new build properties would no longer include gas boilers from 2025.

www.viessmann.co.uk

 

[king of pipes]

Can't see it happening millions are being spent on natural gas hydrogen mix fuels to produce a cleaner type of energy , air source in a old vicarage type building would cost a fortune and the property would need substantial insulation of the walls ceilings and floors it just wouldn't be cost effective . Kop