Integrated pump in a system boiler. Any reason for it?

[richardindorset]

In the system boiler I have, there's an integrated circulation pump. Just wondering what benefit this has over and external pump or if there's a specific reason for one needing to be integrated due to being a pressurised non-vented system?

Does it just make installation easier?

 

[fixitflav]

In the system boiler I have, there's an integrated circulation pump. Just wondering what benefit this has over and external pump or if there's a specific reason for one needing to be integrated due to being a pressurised non-vented system?

Does it just make installation easier?

That's the definition of a system boiler, one with internal pump and expansion vessel. Alternative is a heat-only boiler, with separate pump and expansion vessel (if pressurised) or feed/expansion tank (if open vented). There could be circs eg restricted space, where system boiler lends itself, and it probably makes installation easier, specially on a new-build. Advantage of heat-only is the accessories are easier to access in the event of a problem, and fixable by a DIYer, without needing a gas-safe guy.

 

[richardindorset]

That's the definition of a system boiler, one with internal pump and expansion vessel. Alternative is a heat-only boiler, with separate pump and expansion vessel (if pressurised) or feed/expansion tank (if open vented). There could be circs eg restricted space, where system boiler lends itself, and it probably makes installation easier, specially on a new-build. Advantage of heat-only is the accessories are easier to access in the event of a problem, and fixable by a DIYer, without needing a gas-safe guy.

I my case I am wondering about putting a system boiler into an existing vented system, in order to get a more efficient boiler, on the cheap! (picked up a near new system boiler for almost nothing).

I know it won't like the lack of pressure, (it has a pressure sensor and 'needs' 0.5 bar to operate) but not sure if there's any reason why it shouldn't operate with lower pressure water. It's not like its going to be trying to boil the water!

 

[fixitflav]

I my case I am wondering about putting a system boiler into an existing vented system, in order to get a more efficient boiler, on the cheap! (picked up a near new system boiler for almost nothing).

I know it won't like the lack of pressure, (it has a pressure sensor and 'needs' 0.5 bar to operate) but not sure if there's any reason why it shouldn't operate with lower pressure water. It's not like its going to be trying to boil the water!

If you live in a typical 2-storey house with the F/E tank in the loft and the boiler on the ground floor, a good chance you'll have the 0.5bar. If not, you might be able to adjust the pressure switch, or bypass it. Anything above about 0.2bar should be OK in practice, I'd just try it!

 

[richardindorset]

If you live in a typical 2-storey house with the F/E tank in the loft and the boiler on the ground floor, a good chance you'll have the 0.5bar. If not, you might be able to adjust the pressure switch, or bypass it. Anything above about 0.2bar should be OK in practice, I'd just try it!

Yep, that's what I want to go. We live in a very tall house so I recon I'll be a touch over 0.5 bar! Yes, I know where the pressure switch is and it will be easy to spoof it if needs be... Or lift the header up a bit more!

Bottom line is, we have a old but reliable Potterton which is not very efficient. I got my hands on 2x Glow Worm 30s Energy 7 boilers with a couple of years on them for very little money. So I figured I can swap out the Potterton and keep the other boiler for spares. Should save 20% on gas. Pay for itself in a few months, depending on if I can find a Gas Safe guy to connect the gas of course!

 

[fixitflav]

Yep, that's what I want to go. We live in a very tall house so I recon I'll be a touch over 0.5 bar! Yes, I know where the pressure switch is and it will be easy to spoof it if needs be... Or lift the header up a bit more!

Bottom line is, we have a old but reliable Potterton which is not very efficient. I got my hands on 2x Glow Worm 30s Energy 7 boilers with a couple of years on them for very little money. So I figured I can swap out the Potterton and keep the other boiler for spares. Should save 20% on gas. Pay for itself in a few months, depending on if I can find a Gas Safe guy to connect the gas of course!

Good luck!

 

[richardindorset]

Good luck!

Thanks Fixit.

Just one more thing, given that the new boiler has an integral pump, the exisiting external one can be removed can't it? No point in having both running and wasting leccy.

 

[Madrab]

Depends ... did the installer not mention that when the boiler was installed?

If it wasn't required to add extra head to the system for a specific reason then they should really have removed it at the time the boiler was installed. Sometime a secondary pump can be used where there are extended/elongated feeds to rads far away/high up to aid in balancing the system flow and even out warm up times but if that isn't required then only one pump should be needed.

 

[richardindorset]

Depends ... did the installer not mention that when the boiler was installed?

If it wasn't required to add extra head to the system for a specific reason then they should really have removed it at the time the boiler was installed. Sometime a secondary pump can be used where there are extended/elongated feeds to rads far away/high up to aid in balancing the system flow and even out warm up times but if that isn't required then only one pump should be needed.

Hi Rob, not been installed yet. I have an old vented Potterton that I want to replace with a new system boiler. In theory I can't see why it can't be done, keeping the system vented (so I don't have to change the tank). Hopefully there's enough head to keep the new boiler happy. If not I'll get the soldering iron out!

 

[fixitflav]

Hi Rob, not been installed yet. I have an old vented Potterton that I want to replace with a new system boiler. In theory I can't see why it can't be done, keeping the system vented (so I don't have to change the tank). Hopefully there's enough head to keep the new boiler happy. If not I'll get the soldering iron out!

If your house is anything like typical, no reason why it won't be fine with the built-in pump alone. If the speed is adjustable, use the minimum that works OK.
(you mean blowtorch, not soldering iron!)

 

[Madrab]

Hi Rob, not been installed yet. I have an old vented Potterton that I want to replace with a new system boiler. In theory I can't see why it can't be done, keeping the system vented (so I don't have to change the tank). Hopefully there's enough head to keep the new boiler happy. If not I'll get the soldering iron out!

Ah ok, I'd leave that to the installer. He should be aware of it and know it's there and if it's not needed then it should be removed. No harm in mentioning it, so it's highlighted.

As suggested, it would only be useful if added/extended runs were struggling to warm up properly after proper setup and balancing but that would be down to the installer to sort, that's why your paying them after all.

 

[richardindorset]

If your house is anything like typical, no reason why it won't be fine with the built-in pump alone. If the speed is adjustable, use the minimum that works OK.
(you mean blowtorch, not soldering iron!)

Yep, if both run it will be fine, but it's quite a bit of power to waste if its not needed. I'm doing this to save some money on bills after all!

 

[fixitflav]

Yep, if both run it will be fine, but it's quite a bit of power to waste if its not needed. I'm doing this to save some money on bills after all!

Highly unlikely you'll need both pumps. I would remove the external one. Nothing to stop you leaving the fittings in place in case it's ever needed eg if at some point you go back to a heat-only boiler.

 

[Johntheo5]

Most system boilers have a internal bypass, vaillant's default setting is 2.5M but can be adjusted to a max of 4.5M, if the system pump is pumping into the boiler HEX then at max circulating rate the HEX pressure loss might be ~ 4.0M, depending on the bypass setting then the bypass will be shut at max flowrate if set to 4.5M but at very low flowrates can cause excessive bypassing with very high boiler return temperatures resulting in reduced boiler efficiencies, also most internal pumps wont give more than ~ 5/5.5M head at full flowrate resulting in "only" 1.5/2M available for system circulation.
A heat only boiler has no internal bypass so the external bypass can be set somehere below the max pump head, there are some instances where a 8M pump is required to give the required flowrate through some systems, for whatever reason, if this boiler/pump are replaced with a system boiler then a LLH/CCTs are required with extra pumps/expense.
Also the max flowrate through a system boiler is based on a flow/return of 20C, so a 30kw boiler will have a recommended max flowrate of 21.5LPM, if you wish to run your rads at a lower dT then you may have to install a LLH/CCTs to achieve this, you wont require this with a heat only boiler, high head pum , if the decrease in the required dT is modest, say 15C vs 20C, of course, in most cases the boiler output is way more than the required rad heat requirement so LLH/CCTs not required either with the system boiler.

 

[fixitflav]

John IMO you're overthinking and overcomplicating things. I think the best plan is to install it and look into some of that in the unlikely event that there's a problem.