New Combi - One Pipe System

[doitall]

I'll assume you didn't read my post then

TRVs for one pipe system are not, repeat not bi-directional, so as I said you have the wrong valves.

Ps, I assume he run the new pipes from the boiler to connect into the existing htg pipes in the same place.

 

[mogget]

. However, the valves are bi-directional.

Some TRVs (I suspect the majority, actually) aren't suitable for one pipe systems, not sure which ones though. Maybe someone else knows?

I am now considering asking him to convert to two pipe ASAP as although it will cost more, it seems the only solution.

I would think that if you can possibly afford it, a two pipe system is far superior to a one pipe system in all respects.

I hope it turns out well for you, don't forget to post back and let us know how it went, when the time comes.

EDIT: Doitall beat me to it!

 

[xr4x4]

I assume the pumps on speed one?

 

[doitall]

No normal TRV is suitable for a one pipe system mogget.

You need the special ones with the large nozzle (the same as a low pressure ballvalve nozzle with the larger orifice. )

 

[mogget]

No normal TRV is suitable for a one pipe system mogget.

You need the special ones with the large nozzle (the same as a low pressure ballvalve nozzle with the larger orifice. )

Got it - thanks!

 

[Agile]

With a 22 mm one pipe AND gate or iso valves under each rad then it should work perfectly well and probably without having to change the TRVs either!

The only slight drawback will be that the rads on the return end of the circuit will be a bit cooler than those on the flow end. If set up for a Δ T of about 12 C that will not be much of a problem.

That will only be significant in the coldest weather and will result in the boiler working less efficiently as the flow temp will be too high to give much condensing.

However to automatically controll the flow temperature to maintain best boiler efficiency a weather comp control will be needed ( or a proportional room stat ).

Tony


PS Tell Scruff that its a series connected system and then he will be more happy!

 

[Nige F]

I take your points. I am well and truly miffed. . I am now considering asking him to convert to two pipe ASAP as although it will cost more, it seems the only solution.


John.

That`s how I would`ve done it

 

[doitall]

With a 22 mm one pipe AND gate or iso valves under each rad then it should work perfectly well and probably without having to change the TRVs either!

The only slight drawback will be that the rads on the return end of the circuit will be a bit cooler than those on the flow end. If set up for a Δ T of about 12 C that will not be much of a problem.

That will only be significant in the coldest weather and will result in the boiler working less efficiently as the flow temp will be too high to give much condensing.

However to automatically controll the flow temperature to maintain best boiler efficiency a weather comp control will be needed ( or a proportional room stat ).

Tony


PS Tell Scruff that its a series connected system and then he will be more happy!

You really must stick to repairing boilers agile.

The OP has had a guy in that obviously hasn't a clue about a one pipe system or how it works. Converting it to a two pipe it may or may not work, depending where the new heating flow/return is connected, I can imagine it's been chopped in the nearest part of the existing loop.

I can see the lot getting ripped out and re-piped from scratch.

 

[plumbarius]

Hello Johnny, I presumed the TRVs were fitted on the system before the Combi was fitted, If they were fitted with the Combi that could be the problem they have a very small hole in the valve and there is a lot of restcrition, How was the system cleaned? Power flush or chemicals can you Power flush a one pipe system given you have the same pressure/suction on both pipes to rad I dont know,If the lads on here could answer that out of interest.
I would still take a rad off and see how clean it is, if they are clean remove the TRVs and fit weather compensation or a Honeywell CM901 or CM907 like Agile says. If it worked before it should work now so something has changed, If your Plumber is a young chap he made a mistake that is how we all learn and I would let him correct it.
Thanks Alex.

 

[doitall]

like Agile says. If it worked before it should work now so something has changed, If your Plumber is a young chap he made a mistake that is how we all learn and I would let him correct it.
Thanks Alex.

How about removing a back boiler and fitting a combi boiler in a different location.

 

[Johnny8718]

Thanks for all your replies!!!

The valves were fitted to the one pipe system some years ago by me. I must admit, they havent been overly effective - your explanations may give the reason for this!!



He isnt a young lad, he is very experienced and of course he has had to connect to the system in another location - he's moved the location of the boiler!!

He is back on Friday and assures me that he will sort it. I do understand the differing views on one pipe systems, but have to defend him somewhat in the fact that he has tried at least.....

Xr4x4 - I am told that the pump speed cant be altered. We did consider trying to slow it down. Do you know if there is an option to do so?

I will let you know what happens.

Thanks once again, John.

 

[doitall]

The pump speed has nothing to do with it. The flow into the rads is by gravity circulation from the loop.

You can buy special tees to encourage flow into the rads, but I still think the problem is installation error.

What has he done where the loop was connected to the old boiler

Perhaps a sketch showing existing and modified.