Upgrading gravity hot water to fully pumped

[jonnyp]

I'll need to get a new boiler soon to replace my 20yr old 4 pipe boiler with separate gravity HW and pumped CH open vented system but I foresee a problem with the overflow and vent being on the end of the HW circuit. Boiler is in the garage and has 28mm pipes going up to the airing cupboard on the next floor via several rooms and then up to the loft to the expansion tank.

Problem is I can't see how to convert to a fully pumped boiler system without getting pump-over problems on the HW side. I don't want to have floorboards ripped up to install new pipework to the cylinder as that would involve 3 or 4 rooms. House (and heating) is 40 years old so reluctant to go to a pressurised system but can't see an alternative. Putting a restrictor on the HW flow side would affect the free overflow expansion route so I assume that's not a good idea.

I've looked at answers on various forums but all require the pump relocated to the airing cupboard and new pipework. Other than converting to a pressurised system, the only other idea I have is to reverse the flow on the 'gravity' HW system so that the flow is on the 'fill' side rather than the expansion pipe but not sure if this would be successful and would I still get pump-over.

I'll be getting one or two quotes in from gassafe installers but wanted to familiarise myself with the options before getting someone in.

Any ideas?

 

[SimonG]

Few ways to do it. Your gas safe engineer will know the best recourse for your installation.

 

[Chalked]

Don't worry about it.
Your gas safe installer will know the best route to take.

 

[Chalked]

Don't worry about it.
Your gas safe installer will know the best route to take.

 

[Simon F]

depends largely on where the central heating pipework is.
whats wrong with the pump in the airing cupboard??
where will the new boiler be?
only possible to give full advice with a good look,
which possibly could involve lifting floor boards!

 

[jonnyp]

Thanks Simon. I appreciate it's really difficult without seeing it first hand. New boiler will be direct replacement in garage. CH pipework is not near airing cupboard and there would be no room for pump in the airing cupboard unless above the cylinder anyway. Having done further research, I'm now thinking maybe best to leave it largely as it is (it works well) but join the CH and HW flows and returns in the garage and have two pumps, one on the rads flow and one on the HW return.

I appreciate that the fitters quoting me will have their own ideas but they'll probably all be different (and cost differently) and I wanted to get some idea for myself before getting them in.

 

[joni os]

Avoid two pumps. Make all garage pipework 22mm, S plan on flows with bypass, link HW return to CH return prior to pump and increase height of vent above F&E tank if pump over occurs.
The worst situation if this doesn't work is having to extend feed and vent into garage.

 

[joni os]

Avoid two pumps. Make all garage pipework 22mm, S plan on flows with bypass, link HW return to CH return prior to pump and increase height of vent above F&E tank if pump over occurs.
The worst situation if this doesn't work is having to extend feed and vent into garage.

 

[jonnyp]

Thanks joni. I like the idea but wouldn't there be a concern about keeping a free 22mm flow to F&E tank from boiler when the HW valve is closed? Did you mean fit the pump on the RETURN? Where would the bypass (auto?) go from/to?

Any particular reason why avoid 2 pumps? (I have another new spare lowara ecocirc 25/4 available)

 

[joni os]

Your setup is far from ideal, but you are asking to modify existing with minimum alteration to pipework. As others have suggested, an eyes on evaluation may provide a better and more effective solution. The F&E connections will still function as the HW valve only closes pipework from one side. Pump on return close to boiler.Bypass taken off flow prior to S plan valves and connected to return prior to pump. If pump over occurs you will have to consider relocating F&E connections and have valve to vent air from high point.

 

[jonnyp]

Sounds good. Very useful thanks. It'll be interesting to see if they suggest that during the quotes. I assume the presence of the pump on the return isn't an issue wrt restricting the route for the expansion.

 

[Best]

Sealed system still the best and simplest system by far, so needs your heating person to evaluate its condition. If pipework was done well 40 years ago, it should still be fine.

 

[Vee]

System can be sealed without being pressurised. Leave F&E in place. Cap of vent pipe with manual thumb vent. Fit isolation and non return valves on feed to system. Fit safety controls, I.e expansion vessel and Pressure relief if using conventional or fit with system boiler with adjustable or no requirement for minimum pressure sensing. Used to do this with Worcester Cdi System when customer did not wish to go to pressurised due to old pipework or water main in non practical location in relation to boiler. Allows pump to be fitted in location adjacent boiler with conventional boiler. Avoid two pump as needs control of boiler via relay. Avoid pump on return due to more likely air ingress through vent pipe & pumping over.