Issue with a replacement central heating install- 15 rads!

[theanalyst]

ok guys.
I did an install the other day. It was in a property that is actually 2 houses joined into one house to make a detached (semis). As a result the pipework was from what we could make out, both sides literally joined into one.
I installed a Vaillant 831 as there is one bathroom and one downstairs cloakroom. Although there is 15 rads they are mainly small singles and I have fitted this boiler with no issues on similiar sized houses, apart from adding an extra expansion vessesl on one where the pipe runs were long.

This house doest have huge pipe runs, but here lies the problem as I see it.
We removed an OLD glowworm with gravity HW and pumped CH, one half of the properties upstairs radiators did not get any more than luke warm for the last few years... so I put some cleaner in the old system a few weeks before we started, and then flushed the system with mains water until it was running clear. (a good while>>)

INstalled the new boiler, it has flow and return in 22mm from downstairs until it where hte old circs reduced to 15mm upstairs. Also fitted 15 new trv locvkshield sets.
Anyway, on running it up, one of the furthest radiators away from the boiler would only get luke warm, I have balanced the system to within an inch of its life and also shut them all down except this one and it gets roasting, so its not blocked or an airlock.

I have installed a magnaclean on the system which has been emptied 3 times during running and flushing, so the system is getting much cleaner!!

The crux of it is if I turn the TRVs on the 2 nearest rads down to number 3 (as opposed to 5) then this pesky last rad gets to a proper (equal) temp. If they are on 5 though (with the rest of the house) it only gets luke warm.

I am starting to think the upstairs runs are too long in 15mm>> as the houses were originally piped to be individual systems in 15mm?
i would say the house width is 20 metres total run across the house, and its a standard 2 storey house height, 2 bedrooms each side.

I was thinking if the customer is realy bothered about the last rad, that the only option would be to extend a backbone of 22mm across the top of the house, thereby meaning the flow across there would increase...

Is there anything else anyone can suggest?

Is it possible to increase the pump rate on the 831 for example? I couldnt see it as a setting in level diagnostics tho!

thanks

 

[armourer]

Remove all of the TRV heads and balance just using the lockshields, the first few rads will probably need to be almost closed.

You could also look at matching the pump and fit a secondary circulating pump.

 

[theanalyst]

Remove all of the TRV heads and balance just using the lockshields, the first few rads will probably need to be almost closed.

You could also look at matching the pump and fit a secondary circulating pump.

Cheers mate,
I had all TRVs left on fully open for balancing.I only used the lockshields, I balanced it to within an inch of its life and then it was the TRV tweaking in an attempt to get it to balance.
An additional pump is a good idea!! What do you mean by matching the pump? any input on how I would do it on a combi?

thanks

 

[tamz]

Sounds like you have undersized your pipework.

 

[theanalyst]

Sounds like you have undersized your pipework.

Yes, it does indeed sound like it undersized..!! however it's not my pipework that is undersized... it is pre-existing pipework that the customer didnt want changing due to cost, and we were hoping it would be sufficient.
i have advised him to cure the problem we will need to run a bacbone of 22mm along the spine of the upstairs of the house (where the issue is) so it will be up to him to decide if he wants this doing.
Seems a lot of expense for keeping one TRV on 3.5 instead of 5 though..!!!

 

[stevetheplumber]

id use a bit of inch on that systemthen split to2 x 22
surly if it works with the trv on 3.5 it should work with the ls shut down he same

 

[theanalyst]

id use a bit of inch on that systemthen split to2 x 22

Cheers Steve

Might even go to that length. Although I am pretty sure 22 would sort it, (plus I happen to have a load of 22mm Poly in the van.!!)

 

[theanalyst]

id use a bit of inch on that systemthen split to2 x 22
surly if it works with the trv on 3.5 it should work with the ls shut down he same

that makes a lot of sense, I will try further tweaking those two lockshields!!! Will let you know if it works!!! cheers mate