Converted Semi-Pumped System?

[NigelG]

Hi All,

After much head-scratching and trying to work out what's wrong with the heating system in my son's house (he moved in 3 months ago), I believe some of the problems are due to the location of the Feed and Expansion pipes. This is most noticable when trying to fill/drain the system, as air keeps getting trapped.

From what I can work out, the original system must have been semi-pumped, with gravity fed heating to the hot water storage tank. At some point over the last few years, a new boiler has been installed, inside the integral garage, with a typical 'S' system arrangement, with the pump and 2 x two port motorised valves alongside it. However, there are no F&E pipes in this location, just an automatic air valve on the boiler return. They remain in the first floor airing cupboard on the feed and return pipes of the tank.

I have to admit that running F&E pipes to the boiler area would be rather tricky and they would also be something like 10 metres long (due to locations of boiler and header tank). However, I'd appreciate some advice as to whether this is the most likely cause of the system trapping air in the radiator circuit.

By the way, I already discovered that whoever installed the new boiler managed to cross the feed and return pipes, as all the rads are heating from the lockshield valve side (sorting this out next week).:sad3:

All thoughts gratefully accepted.

Regards
Nigel G

 

[RoryD]

I'm a little confused here, You have an SPlan but no feed and expansion tank (not pipes)? Is there a pressure guage on the boiler or elsewhere on the system - there will be a large red vessel accompanying it? What boiler does he have

 

[ecowarm]

Incorrectly installed feed and vent will cause air to be sucked in to system and pumping over, both will quickly cause the system to block with sludge and possibly rot from the inside, pin holes on the rads and pipework.
Can the pump and motorised valve (s) be moved to the f&e pipe location?
Can you convert if to a sealed system and do away with the feed and expansion? You will need to check the boiler instructions to see if this is ok. If you are not competant to do this work then call in a professional.

 

[NigelG]

Hi Guys, In answer to RoryD, yes there is a F&E tank, but the problem is that it connects into the water heating circuit where the tank is, not where you would expect. The boiler is a Potterton, but I can't remember the model at the moment.

Ecowarm, I'd tend to agree with your comments about an incorrect installation. Unfortunately, to move the pump/valves into this location would also mean I'd have to redirect a fair length of the heating circuit. It rather sounds to me that the best option is to look at rerouting the F&E to the correct location and replacing one of the current connections (by the HW tank) with an auto-bleed valve.

Regards
NigelG

 

[ecowarm]

I would look at converting to a sealed system

 

[NigelG]

Thanks Ecowarm, I'll check out the boiler details and see if this is a possibility. I confess to being rather perplexed as to how the original installer (whoever it was) managed to get it so wrong.

Regards
NigelG

 

[stevetheplumber]

ift he boiler has an overheat stat then its usually capable of being sealed you say it was changed so chance are it can be
it will be easier than running new feed and exspansion pipes
especially if it in a garage were looks are not so important
youll need vessel prv and filling loop and some vents for the cylinder circuit

 

[NigelG]

Right, bit more investigation done. The boiler is a Gloworm Flexicom HX, which according to the specifications is quite capable of running a sealed system (can't think why I thought it was a Potterton originally, must be my age!). I'm confident I can deal with the conversion, but would appreciate someone confirming what size expansion vessel would be needed.

The static pressure will be around 0.9bar, with a system capacity of 85 litres (as near as I can calculate it).

Regards
NigelG

 

[ecowarm]

Nigel look here [DLMURL]http://www.rwc.co.uk/public/expansion/xves-001.pdf[/DLMURL]

Go down to heating vessels- easy fit systems and size to boiler output, its easier.
But if you want to work it out the formula is on there aswel.

 

[NigelG]

Thanks Ecowarm, very useful document. I'll have a read through this evening and come back if I have any questions.

Regards
NigelG

 

[RoryD]

No probs having cold feed going to airing cupboard but it should be close coupled just after the Vent pipe and within 150mm from, and before the pump

 

[doitmyself]

I believe some of the problems are due to the location of the Feed and Expansion pipes.

Where do they connect into the system?

Is the pump on the flow or return?

They remain in the first floor airing cupboard on the feed and return pipes of the tank.

Are you saying that the feed is on the flow and the vent on the return - or the other way round?

Whoever installed the new boiler managed to cross the feed and return pipes, as all the rads are heating from the lockshield valve side (sorting this out next week).

If you have wheel head type valves, all you need to do is swap the wheel head to the other end - the valves are identical. If you have TRVs, check that there are two arrows at 90° on the valve body. If there are, it doesn't matter which end the TRV or LS valve goes. All a LS valve does is set the maximum flow through the rad. What goes in must come out!

 

[NigelG]

RoryD, only the HW tank is in the 1st floor airing cupboard, with the F&E pipes connected either side of the heating coil. Everything else is in the ground floor garage!

Doitmyself, see above for the F&E pipes. Pump is on the return pipe to the boiler (wrong place, I know and already on the list of things to sort out).

The TRV's are of the older type and only suited to the inlet side of the rads. Some of these are showing signs of age and sticking down, this could partly be due to the constant system pressure being put on them with the feed coming in through the LS.

I'm already sourcing the parts for converting to a sealed system and have a list of other things to correct, whilst I've got the system fully drained.

Thanks again for all the advice guys.

Regards
NigelG

 

[tamz]

The pump being on the return is not necessarily wrong and may have been put there deliberately to save running new pipes eg FEP type conversion.
To explain the reasoning and how it should be set up would take me too long as you need to have a really good understanding of how heating systems work to be able to grasp it.
If you have the time and the patience just alter the system to what you know.
Btw fyi there is not such a thing as a semi pumped system.......(it is called a gravity)........but i know what you mean.

 

[RoryD]

I give up,

 

[NigelG]

Hi All,

Well, after a few days work, we now have a successfully working sealed system and the house is all 'warm and toasty for the first time' (comment from son!).

Just one remaining question: Their mains pressure is around 2.5 bar, but the sealed system must be charged at 1 bar (boiler manufacturers spec). This was not a problem for me, as I just released any excess pressure via the fill-loop valve. Would it be reasonable to install a pressure reducing valve on the mains supply, just before the fill loop, just to make life easier for them to top the system up if required?

Regards
NigelG

 

[ecowarm]

It's possible but I think unnessessary

 

[NigelG]

Thanks Ecowarm, It was only a passing thought, but I guess he can do what he normally does when not sure what to do......call Dad!

Regards
NigelG