No heat

[emphasis303]

Hello all,

Have a one pipe system, thats been working fine for over 3 decades! Recent issues with upstairs working and downstairs not working.

Have had a new pump new expansion vessel and new heat exchanger and 6 new rads and valves - all faulty luckily covered by homeserve.

Been powerflushed waters clean, all rads have water gushing out.

The problem is the rads downstairs even the new ones do not want to get anywhere near hot, just warmish.

Checked usual suspects, balancing and trvs etc but still no joy, only when I turn all rads off then start one by one turning them on the individuals get hot if i open them all even a quarter turn each then ive got a load of luke warm rads.

Any ideas? 28mm from the boiler down to 22mm 1 metre away then 15 into rads, really strange has never been like this in the last 2 decades of ownership.

Boiler is a vaillant ecomax 637, boiler seems to be absolutely fine according to about 5 different vaillant engineers. Only thing can think of is the engineer set the heatouput to 28kw boiler is i think 35kw, 19 rads, have a megaflow cylinder no issues with hotwater.

 

[Terry lambert]

Are the new TRVs the correct ones for a one pipe system? If not, could be your problem

 

[emphasis303]

Yeah they are specifically for a one pipe system, the plumber who changed them had to wait a day for them to come in, rads even with normal valves have the same issue.

Thanks

 

[Dean744PiN5]

when was the boiler fitted?

 

[emphasis303]

2003ish

 

[emphasis303]

sorry think its 635e not valiant 637

 

[simond]

You can't powerflush a one pipe system with any chance of success; the water doesn't go through the rads in the manner needed to clean them.

19 rads and one expansion vessel?

Turning individual rads on and off on a one pipe will do nothing. The water only circulates into each rad by lower density led gravity.

If you have two separate one pipe loops, turn the upstairs off and see how the downstairs goes. Sounds like very low flowrate round downstairs loop, could be airlock or partial blockage.

 

[emphasis303]

Thanks for your reply, I should have mentioned If I turn upstairs rads off, downstairs rads do get warmer but still not hot enough.

 

[emphasis303]

An airlock on a sealed system?

If there is a blockage and a power flush isn't curing it, any ideas what will apart from ripping up floorboards to replace pipework?

Thanks

 

[simond]

If its a one pipe, the the rads should be connected alternate top and bottom format.

The valves should be one pipe specific, which means the bodies are broadly twice the diameter of a standard TRV.

The first thing you need to do is ignore the rads, and feel the one pipe where it leaves and returns to the boilers from the first floor, and similarly from and to the ground floor rads. Both sets of pipes should be really hot where they start and 10-20C lower where they return.