Prima 50F - V.short 'burn' time on Hot Water setting

[leftofcentre]

Hi there, hope you can help.

I have a Potterton Prima 50F, about 3-4 yrs old. (Just bought the flat that I was renting so have inherited the system)

I left the flat vacant while doing a ski season for 5 months recently and switch the heating and hot water off completely while away. Upon return the boiler would fire up perfectly but only run for 60-70 seconds before shutting down.

BG man came on his initial Homeserve visit and diagnosed that the pump had seized due to inactivity; he got it going, did the rest of his checks and left with the water and heating running perfectly.

However, I have since discovered that if I run only the hot water on its own, the boiler fires up, runs for 30-35 seconds and the shuts down for about 3 minutes before firing up again and running for a further 30-35 seconds. This continues for the entire programme.

The immersion is not on, the existing water in the system is only warmish and the boiler thermostat is set to 4. As a result the water gets hot but never really hot and I can't help thinking that the repeated cycling on and off will wear out the boiler quicker or be inefficient in gas use and in heating water, be more polluting or all of the above.

Unfortunately I can't remember if it was doing the same thing before I went away.

Thoughts anyone? Thanks in advance.

 

[gas4you]

Could be the pump stuck again as you don't say that he actually replaced it. Could be 2 port or 3 port valve fault, but you haven't told us if you have them or which it is.

 

[leftofcentre]

BG man didn't replace the pump; just tapped it to get it moving again then turned it through its different speeds to ensure that it was properly functioning.

The boiler runs constantly without cutting out when the heating is switched on, the problem occurs only when its on hot water only.

I don't know what a 2 or 3 port valve is I'm afraid.

Thanks.

 

[pampliers]

BG man didn't replace the pump; just tapped it to get it moving again then turned it through its different speeds to ensure that it was properly functioning.

The boiler runs constantly without cutting out when the heating is switched on, the problem occurs only when its on hot water only.

I don't know what a 2 or 3 port valve is I'm afraid.

Thanks.

STOP MESSING WITH WHAT YOU DON'T KNOW AND LEAVE IT TO THE PROFESSIONALS SON

 

[gas4you]

Lets forget about pump then.

Near your hot water cylinder usually, after the pump you may have 2 silver metal boxes, or plastic, with 2 pipes connected to them, or one box with 3 pipes on it. These this will be your zone valves. If 2 x 2 port then one will be heating and one will be hot water. Check hot water one is working/opening. Should have a manual lever on it to open.

Another cause could be somehow an air lock in hot water side. Is there an air vent near hw cylinder?

Have you checked f&e tank has water in it?

For some reason the water isn't circulating around the hw circuit it seems.

 

[leftofcentre]

STOP MESSING WITH WHAT YOU DON'T KNOW AND LEAVE IT TO THE PROFESSIONALS SON

Err... did I say that I had messed with it? All I am asking the experts on here who have more that 3 posts to their name is whether this is normal or not. If it is not then I will get BG out again. If you have nothing useful to contribute then dont bother posting.

 

[corgiman]

STOP MESSING WITH WHAT YOU DON'T KNOW AND LEAVE IT TO THE PROFESSIONALS SON

Err... did I say that I had messed with it? All I am asking the experts on here who have more that 3 posts to their name is whether this is normal or not. If it is not then I will get BG out again. If you have nothing useful to contribute then dont bother posting.

fancy your own dad talking to you like that



Ignore him OP he is new, and nearly all new professionals tell diy'ers to "leave it alone and call someone in" on anything

Pamper this IS a diy website

 

[leftofcentre]

Gas4u.

Pump is running fine although case is extremely hot.

I have two valves. A Tower switched to manual open which is feeding the cylinder and a Honeywell one set to auto feeding the rads.

Yes there is an air vent next to the cylinder and it is not covered.

The BG man checked the f&e tank and I have just looked again and the is water in it and the ball cock is functioning properly.

The hot water taps and the shower are running hot just not very hot.

 

[corgiman]

Gas4u.

Pump is running fine although case is extremely hot.

I have two valves. A Tower switched to manual open which is feeding the cylinder and a Honeywell one set to auto feeding the rads.

Yes there is an air vent next to the cylinder and it is not covered.

The BG man checked the f&e tank and I have just looked again and the is water in it and the ball cock is functioning properly.

The hot water taps and the shower are running hot just not very hot.

Could be the boiler Stat

Call BG and let them sort it out, why have a dog and bark yerself

 

[gas4you]

Pump being extremely hot points to a fault with circulation also. Is there a balancing gate valve on the hot water flow/return near the cylinder that could be opened fully?

An outside chance could be a sludge blockage in the hw circuit as this could also have contibuted to the pump siezing in the first place.

Pump could be spinning but not circulating, but then I wouldn't expect all the rads to get piping hot if this was the case

 

[leftofcentre]

Yes there is a gate valve near the return that has a slot head adjustment on it. I just touched it and heard what sounded like a load of sediment rushing through nearby pipes. A few drops of brown water also leaked from the slot head screw.

 

[leftofcentre]

Gate valve appears to be fully closed.

By my thinking that means that the pump is trying to force water into a cylinder that is already full as the water in the cylinder has nowhere else to go.

??

 

[leftofcentre]

Have shot a video of the pipe arrangement. The silver valve with the slot head screw that the video lingers on is the one that is shut tight.



I'm thinking from reading other threads that this shouldn't be closed and should be open to allow the system to balance correctly.

Is that right? Please advise as if all it needs is a tweak from a screwdriver I don't want to have to call out a plumber.

Thanks.

 

[Gasguru]

The valve directly underneath the Tower zone valve may be partially blocked.

Be aware that opening/closing it may well result in leaks.

It has probably be set partially closed to balance the heating and hot water circuits.

Opening fully and allowing the water to clear it out for a while may solve the problem.

If your on a contract let them do it but muck/debris in the system is not usually covered by the policy.

 

[gas4you]

One of the strangest looking pipe work set ups I've come across recently

There seems to be 2 flows going to the coil flow, one from the zone valve and one from above the 15mm ball-o-fix valve. I can't work out what that is doing there. Seems in the wrong place to be a by-pass and won't really help as a balancing valve.

Where does the 15mm pipe go above the ball-o-fix?