underfloor heating causing boiler to cycle continually

[gwc1]

Hello all im new to this forum and looking for some help that would be greatly appreciated. Ive recently had an extension and had wet under floor heating on a dual manifold with pump installed into a 25square meter area also had two additional rads installed all running off a vaillant ecotec plus 837 combi boiler.The system has two motorised valves controlled by room stats and a digital programmer. My problem is that when the central heating is running independently the two new rads in the ground floor extension take forever to warm up and when the underfloor heating is run independently it causes the boiler to overheat and shut down after only a minute or so it will continue to cycle on and off without the ufh reaching temp. If both rads and ufh is run simultaneously the boiler does not cycle. All valves on the uhf are open to the correct settings its as if I don't have sufficient flow through the boiler which im guessing at. ive turned the pump on the uhf to max to no avail also ive tried opening the flo valves wide open and also filled the uhf with a hose trying to release any locked air which wasn't the case. Ive also stipped the central heating pump to make sure it wasn't gunked up which it wasn't and it is spinning freely .Hopefully I haven't made it sound to confusing and any words of wisdom would be welcome . Thanks

 

[Dan Robinson]

Have you range rated the boiler to the correct heat load of the house?

28kW is mental. for most properties.


Set the D.0 parameter to something like 12kW (guessing at your house size).

 

[RickMoore]

Also give the anti-cycle timer a higher value. About 15-20 mins should be about right. Aa for the rads that aren't getting hot, the system did get re-balanced by the installer didn't it ?

 

[Boilerman2]

If the UFH was simply added to an existing radiator system, then I am not suprised to hear of your problems UFH needs to be integrated properly usually needing it's own circuit and pump

 

[gwc1]

Have you range rated the boiler to the correct heat load of the house?

28kW is mental. for most properties.


Set the D.0 parameter to something like 12kW (guessing at your house size).

Hi Dan no I haven't range rated the boiler I live in a three bed semi. The boiler was already installed when I moved in, its about 5 years old. Is it easy to change the parameters . Thanks for the reply

 

[Dan Robinson]

In that case I would set it so 9 or 10 and try from there.

How it is done is in the manual.

 

[gwc1]

Also give the anti-cycle timer a higher value. About 15-20 mins should be about right. Aa for the rads that aren't getting hot, the system did get re-balanced by the installer didn't it ?

Hello Rick how do I go about adjusting the anti cycle timer is it something a plumbing novice like me could do. No as far as I can work out the rads didn't get rebalanced when I had the build done the builders own plumber installed the system and bodged quite a bit of it ie thermostat above rad no insulation between screed and wall and now hes telling me its operating as its supposed too. So im loathe to let him near it now and have told him im holding payment to pay for a more competent plumber to resolve.Unfortuantely I cant get any plumbers to come out to resolve it there all fully booked or aren't interested in taking someone elses job on which is the impression I get. Cheers

 

[RickMoore]

As per the range rating, setting the anticycle time is also in the manual.
If you loom in the faqs at the top of the plumbing and heating section there is a good guide on balancing so long as you can work a spanner and a thermometer you should manage fine.

 

[Dan Robinson]

This time of year is mental. Anyone worth their salt is going to have a week or two's waiting list unless they happen to be passing.

 

[Agile]

Your job is not particularly urgent so waiting a week is not the end of the world.

Its also important what you asked them to do.

If rads are added then the whole house/zone will need rebalancing and because it takes a while for any adjustments to take effect this can easily take 2-3 hours.

Then, even now, many are not very familiar with UFH and particularly with how to balance that within a system.

I would never advise anyone to let a builder employ a plumber but instead would recommend a heating engineer is engaged working directly to the owner. But that advice is too late for you.

Tony

 

[gwc1]

Your job is not particularly urgent so waiting a week is not the end of the world.

Its also important what you asked them to do.

If rads are added then the whole house/zone will need rebalancing and because it takes a while for any adjustments to take effect this can easily take 2-3 hours.

Then, even now, many are not very familiar with UFH and particularly with how to balance that within a system.

I would never advise anyone to let a builder employ a plumber but instead would recommend a heating engineer is engaged working directly to the owner. But that advice is too late for you.

Tony

Hi yes waiting a while isn't a problem finding someone with experience of ufh committing to taking a look seems to be. Do you know of anyone you could recommend in the Watford area. Thanks

 

[gwc1]

As per the range rating, setting the anticycle time is also in the manual.
If you loom in the faqs at the top of the plumbing and heating section there is a good guide on balancing so long as you can work a spanner and a thermometer you should manage fine.

Cheers Rick and Dan I've made the adjustments you suggested to no avail unfortunately I'll give balancing the system a go while I try and get a plumber in sounds like that should cure the radiator problem. Thanks

 

[RickMoore]

Range rating and changing the anticycle time should have sorted the cycling issue, are you sure you did it right ?

 

[gwc1]

Yes the boiler was set to its max 28 kw and I've set it to its min which is 12 the anti cycle was set at 20 already I'd have to double check tonight to make sure it's the correct one I've altered I'm pretty sure it is. It did take longer before the cycling started 4 min as opposed to 2 and only happens when the uhf is on independently. Cheers

 

[Agile]

I cover the Watford area myself, but somewhat hesitant on account of the situation that seems to have arisen.

Also that sorting it out can be quite time consuming and a half day charge at our rates may not be what the builder's plumber ( who could be East European and working at very low rates for all I know ) will be expecting to be deducted from their contract price.

A further problem is that your boiler has a very high output power compared with the heating load and in particular with the UFH zone which might be about 2.5 kW which will always cause severe cycling with a boiler with a minimum power output of 12 kW !!! Careful fine tuning of the settings might minimise the cycling but a 12 kW output cannot be absorbed by 2.5 kW heating circuit!

Not really relevant, but I call myself a boiler engineer rather than a "plumber".

Tony