Project Overview
| Location | Ascot, Berkshire (SL5) |
|---|---|
| Call-out | Emergency — heat pump fault, no heat going to the hot water cylinder |
| System | Heat pump with a backup Vaillant ecoTEC Plus 637 system boiler, hot water cylinder and Danfoss motorised valves in a plant room |
| Work completed | Heat pump bypassed so the boiler heats the cylinder; hot water restored on the same visit |
| Next step | Return visit booked for a full heat pump diagnosis |
The Challenge
A homeowner in Ascot called us out as an emergency heating engineer on a Saturday because of a problem with their heat pump. The property has a hybrid setup: a heat pump as the main heat source, plus a gas system boiler in the same plant room that can also heat the hot water cylinder.
When the heat pump stops working and the controls do not hand the cylinder over to the boiler, the house loses hot water even though a perfectly good boiler is sitting on the wall. The priority was to get hot water back that day, safely, without guessing at a heat pump fault that needs proper diagnosis.
The Solution: Bypass the Heat Pump onto the Boiler
On arrival we checked the plant room: the heat pump, the Vaillant ecoTEC Plus 637 system boiler, the hot water cylinder and the Danfoss motorised valves that decide which heat source feeds the cylinder.
Rather than leave the household waiting for a heat pump repair, we bypassed the heat pump so the boiler came on to heat the cylinder. Hot water was available again before we left, using equipment that was already installed and working.
Why Bypass First and Diagnose Later
A heat pump breakdown can come from the outdoor unit, sensors, flow problems or the controls. Diagnosing it properly takes time, and an emergency call-out on a weekend is not the moment to start replacing parts on a hunch. On a hybrid system the faster, safer win is to put the boiler in charge of the hot water first:
- Hot water the same day: The bypass got the cylinder heating again on the first visit, rather than leaving the family without hot water until the heat pump could be repaired.
- A boiler with capacity to spare: The data plate shows the ecoTEC Plus 637 is rated up to 37 kW for central heating, so it can reheat a cylinder quickly on its own.
- Valves that control the handover: The Danfoss motorised valves set which heat source reaches the cylinder. Getting them to route boiler heat to the cylinder is what makes the backup work.
- No guesswork on the heat pump: The heat pump stays out of the hot water circuit until it has been diagnosed, so a fault is not made worse by running it.
The Repair Process
- Plant room check: We looked over the heat pump, system boiler, cylinder and motorised valves to understand how the heat sources were connected and why the cylinder was not being heated.
- Heat pump bypass: The heat pump was bypassed so the Vaillant boiler could take over heating the cylinder.
- Hot water restored: The boiler came on and heated the cylinder, giving the household hot water again on the same emergency visit.
- Next steps agreed: We booked a return visit on Monday to fully diagnose the heat pump, or to set the controls up so the boiler works with the cylinder properly rather than through a bypass.
The Results
The Ascot household had hot water back on the same weekend call-out, heated by the existing Vaillant ecoTEC Plus while the heat pump is off the hot water circuit. Nothing was replaced on a guess, and a proper heat pump diagnosis is booked for the following working day.
Recommended Follow-Up
- Full heat pump diagnosis: A return visit on Monday to find the cause of the heat pump fault and quote for the repair. Read more about our heat pump servicing and repairs.
- Boiler and cylinder controls: If the heat pump cannot be repaired straight away, the controls can be set up so the boiler heats the cylinder properly through the programmer, rather than relying on a bypass.
Heat Pump Breakdown Questions
Can my boiler heat the hot water if the heat pump breaks down?
On a hybrid system with a boiler and a heat pump serving the same cylinder, usually yes. An engineer can bypass the heat pump or change the valve and control settings so the boiler heats the cylinder until the heat pump is fixed — exactly what we did on this Ascot call-out.
Do you cover heat pump call-outs around Ascot?
Yes. Talis covers Ascot and nearby Virginia Water, Wentworth, Windsor and Bracknell for heat pump faults, boiler breakdowns and hot water problems. If your backup boiler is due for replacement, see our Vaillant ecoTEC Plus installation in Ascot.